Detecting Edited Images

[Frank_Rizzo]

How easy is it to check if an original picture has been edited? Are there any programs out there which can scan an image and indicate where exactly an image has been edited?

The reason I ask is because I have spotted a competition site which is based on identifying where a missing image was, and I'm concerned that some may be using technology to cheat!

The competition is similar to 'spot the difference' where two pictures are shown but one has been edited - like a dragon has 3 claws in one picture, 4 in the other, a daisy is yellow in one picture blue in the other etc.

This particular competition shows a picture of a crowd at a widgetfest. The widget has been airbrushed out of the picture and you have to guess which person in the crowd was holding the widget.

I'm sure some unscrupulous entrants may be using clever scanning programs, or just painstakingly zooming in 20x and looking for out of place pixels.

What do you reckon? Easy for some to cheat or not?

[eggy ricardo]

I personally would firstly make sure the editing is of the best possible quality to make it as un-obvious as possible, and then maybe reduce the quality or size of the image or something so that any iffy pixels blend in.

There may be a better way but thats how i'd do it.

P.S. You could also use some of the techniques outlined in other threads to make it more difficult for people to save your pictures.

Cheers
Richard

[Robin_reala]

In photoshop/paintshop you can do a difference combine on the two images. Any bits that are the same will appear black, any differences will stand out. Tech sites use the same technique for comparining reference images against images rendered through a manufacturer's driver, to detect 'cheating' in the driver.

For someone who knows you can do it, it's a trivial job. 1 mins work at best.

[Frank_Rizzo]

There is only one image though. It has been edited and the challenge is to use skill and judgement to determine where the widget was before it was removed.

Can't compare the two images as the original is not shown until after the results are posted!

I'm concerned that some may be using technology to find the answer, whilst regular joe competition using his instinct and luck is at a disadvantage.

Try it. Find an image of a crowd scene where some people are wearing hats.

Now edit the picture so that one of the hats is airbrushed out.

Ask a mate to look at the airbrushed picture to see if he can guess which person was wearing a hat and is not now.

BTW, the competition has prizes running into $100,000's. I'm sure some organised crime are on the scene!