The Photographic Science of Detecting Fake Lottery Tickets

http://www.hackerfactor.com/blog/?/archives/478-Fool-Me-Once.html

by ecaron • 14 years ago

254 49 14 years ago

Bud• 14 years ago

What's funny about this to me is that the "04 02" reveals the fake without any kind of photographic analysis whatsoever. The numbers are supposed to be sorted smallest to largest. A valid ticket would read "02 04".

bri3d• 14 years ago

The author mentions that anomaly in the article, but goes on to assume that the sorting is picked by the state printing the ticket (probably for the benefit of being able to continue the case study).

I also noted that the differing color of the "04 02" in that image can be spotted with the naked eye if zoomed in - no advanced analysis techniques necessary.

I think the techniques used were far more interesting than the particular case study - while the media and non-camera-original nature of the images made the author's most basic techniques somewhat ineffective, the fakes were overall very poorly executed.

scoot• 14 years ago

If it were the case that the numbers on this ticket were unsorted, you would expect all of the rows to be unsorted, whereas everything except 04 & 02 are in order, including the numbers that follow in the same row. Still interesting to see the "forensic" approach to this.

FaceKicker• 14 years ago

Slightly related, I was wondering how the actual lottery tells if your ticket is real - do the machines record your ticket's serial number and number(s) chosen and then send the info to the lottery HQ? Or do the lottery machines compute an HMAC of some kind and encode it in the serial number on the ticket itself?

excuse-me3• 14 years ago

I don't know about this US lottery specifically but in most systems everything is recorded at HQ. Not just the numbers, but the place, the date and time, serial number etc

That way they can also check with CCTV.

It's an interesting topic in database design because the link to the store may fail at any time (remember lotteries started years ago on dialup) and you must not have an issued-unrecorded ticket at any point in the process

simcop2387• 14 years ago

From my own experience with buying them, they solve that by saying "machine is down, i can't print any tickets". Not a very high tech solution but it certainly solves that problem completely.

kijin• 14 years ago

Then why did it take so long for them to announce how many winners there were? First they said "at least one", and then they said "three". If everything was stored in a central database, they could have found out the exact figures (and a lot more) as soon as the last winning number was announced.

Maybe it's due to lack of coordination between states? Or maybe they need to do fraud checking, etc. by watching CCTV footage from the point of sale?

stephengillie• 14 years ago

In the US, each state hosts its own lottery program. Mega Millions and Powerball are programs where states have teamed up to pool their resources and gambling markets.

I've sold Washington State's "lotto" tickets, and you're entirely correct about the reliability of the system - if the device can't connect to servers in Olympia, tickets can't be sold.

CCTV is up to the retailers here, though it's entirely possible that CCTV is a requirement to be an eligible lottery vendor.

jbri• 14 years ago

The lottery HQ has records of all tickets for a particular lottery, which gets checked against when you claim a prize.

I'm not sure whether the has-this-ticket-won-anything machines phone home to check it against those records, or whether they just assume the ticket is authentic and leave the proper verification for when a prize is claimed.

fragsworth• 14 years ago

Considering they can tell which vendor sold a winning ticket, they must have a central database logging the numbers chosen for each ticket. Also, considering the amounts of money involved, I can't imagine them doing anything less secure.

gergles• 14 years ago

For "online" games (like this one), your picks are transmitted to the lottery office which stores them and then transmits the serial number back to the terminal, which prints the ticket. This prevents a ticket from being issued that the lottery's central computer doesn't know about.

When it is time to verify the ticket, they simply send the serial number to the lottery central computer and that computer sends back the payout command (and invalidates that serial number from being paid by any other terminals.) The retailer is supposed to do some basic sanity checking for small prize amounts (is the ticket really on lottery paper, etc.) and obviously for larger prize amounts, there are several other methods to verify the authenticity of ticket stock that aren't public knowledge.

3pt14159• 14 years ago

The lottery machine creates a random number that is attached and encoded to your ticket and both the number, and the random bit are sent to HQ.

ChuckMcM• 14 years ago

In California at least one ticket was verified by closed circuit video of the person buying it.

K2h2• 14 years ago

not directly related, but this made me remember some reading I did awhile ago on EXIF analysis.

a really cool tool for EXIF http://www.sno.phy.queensu.ca/~phil/exiftool/

hardy263• 14 years ago

Can you use Photoshop filters to do this, or are there more professional programs to do so?

biot• 14 years ago

Is it possible to reverse engineer the image such that it passes all tests? Knowing the various algorithms that could be used, what would be involved in constructing the modification such that it doesn't reveal evidence of any modifications?

One thought would be to actually render an entire scene in something like POV-Ray. Imagine if something like this rendering http://www.povray.org/community/hof/chado.php contained a winning lottery ticket on the table. If you save the rendered image using the same compression algorithm and same EXIF heading information as a camera, how would one tell the difference?

cuu508• 14 years ago

I imagine it would be hard for renderer to fake all subtle qualities digital camera introduces. Things like "colors too clean", "noise too uniform", "geometric distortion doesn't match any existing lens" would turn up.

In this specific case I think I'd print a fake ticket with dot matrix printer and take photos of it.

sneak• 14 years ago

I imagine that getting one's hands on blank lotto ticket paper stock roll is probably beyond the scope of this "hack".

K2h2• 14 years ago

I have worked so hard to completely replace dot matrix that I am actually trying to think were I could get access to one and am coming up blank! Many receipts are now the crappy thermal paper that magically disappers from being left on the dash.. Its like magic in the retailers favor...and just about everything else is laser. Where would you get the dot matrix?

gigantor• 14 years ago

From the comments, you can reprint the ticket with a receipt/laser printer and take pictures of the copy, losing the artifacts. Depends on the length of trouble you would want to go through to reproduce a hard copy document.

kapgoals• 14 years ago

Not for nothing, but if you merely zoom in on the picture you can tell that the 'winning' line is a different color with the naked eye. And if you want to 'prove' this, a 10-second color replacement in photoshop does the job: http://i.imgur.com/7Mg4z.png

delinka• 14 years ago

To fake a lottery ticket for posting online, it'd be much easier just to print a fake ticket and then photograph it. I suppose, however, that the purpose of doing it digitally is to practice skills and "because I can."

To fake a lottery ticket for claiming a prize ... well, that'd be fraudulent and would result in loss of freedom for quite some time.

greendestiny10• 14 years ago

There is nothing scientific about any of these tests. What's a 'high' ELA or 'low'? The thing that triggers a 'positive' seems to be only the authors intuition. While some of the tests might show something, I'm pretty sure ELA is absolute garbage - you can't separate the number of needed resaves because of the content frequencies from number of times it has already been resaved.

sliverstorm• 14 years ago

What, may I ask, makes a test scientific?

greendestiny10• 14 years ago

You don't need to get technical about it, but I think most people would expect any test described as scientific to be objective.

pazimzadeh• 14 years ago

For one, there should be a control. In this case, analyzing another ticket that has not been faked, but preferable he would not know if the control was real or not.

http://en.wikipedia.org/wiki/Blind_experiment#Double-blind_t...

drx• 14 years ago

He used PCA as well as ELA, making your first statement unfounded.

greendestiny10• 14 years ago

While the result of the PCA is quite well defined, there is nothing well defined about the inferences he draws from that. In the end it shows a marked difference in the suspicious area, but there is no proof that the technique will only show those results on tampered areas.

If you can simply run filters until the suspicious area 'looks a bit different' and thats your success criteria, you haven't proven anything.

maurits• 14 years ago

One basically looks for roundings caused by quantization and places in the image where the compression (again quantization) is either inconsistent or non-optimal.

A nice tutorial (and a lot of articles) can be found on the Dartmouth site of Hany Farid.

http://www.cs.dartmouth.edu/farid/downloads/tutorials/digita...

Personally, I have had very very mixed results with this method, and never managed to model it correctly. Interpreting results always was a very human job.

greendestiny10• 14 years ago

I understand the theory and I certainly agree resaving jpegs will reduce the error level. If you have an undoctored image to compare it to, you could probably use that to determine which parts have been changed. But given only an image that may or may not have been doctored the error level will vary so much with the image content that it won't be meaningful.

jonah• 14 years ago

Simply blowing the contrast out in Photoshop makes the fakery pretty apparent too: http://i.imgur.com/6niwJ.png

user0398• 14 years ago

I find it utterly frustrating that a scientific seeming article would end with this conclusion:

"A single algorithm can trigger false-positive or false-negative results... if something is really real, then it should pass everything."

How you going to be so thorough about detecting a crappy photoshop job and then trip over your own words in the conclusion?

morsch• 14 years ago

This site has a GIMP script for doing Error Level Analysis: http://sites.google.com/site/elsamuko/forensics/ela (After saving it to your ~/.gimp-2.6/scripts folder, the tool hides in the Image menu.)

I just tried it on a couple of my own images, the results are very interesting.

The Photographic Science of Detecting Fake Lottery Tickets

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