If an image is tampered with some additional content, how to remove that additional content from the image in Java?

Question

I want to know if there is any solution for the following scenario:

I have an application which uploads the files, after scanning and transcoding them, onto a server. Suppose, an image file is being uploaded which has been tampered with some additional contents over it. Now, as the uploaded file is illegitimate, I want to remove the additional tampered contents and upload just the original part of this image file. Is it possible to do so in Java?

Thanks.

Answer 1

It's not possible to detect in the general case, but there are some heuristic methods available to determine whether an image has been edited. Try using the tools at http://imageedited.com/ to get an idea of what's possible.

Removing the edit is a much more difficult problem, which is probably impossible with current methods.

Answer 2

I'm just speculating here, and I don't know how well it would work in practice, but you could do it if you limit to specific sources of tampering. E.g., suppose you want to remove the logo added to an image by memegenerator.net.

You know in advance what the text looks like and where it is. Create a transparent png template that matches the text. Then sum the differences between the image and template pixel colors, multiplying each by the alpha of the template pixel. Since for this particular logo, it's basically white (although it seems to have a thin black shadow) you would get false positives for a picture with a white part there, so you'd also need to verify that the surrounding pixels are (within a tolerance) not white. It's not clever but it could work for certain sites.

For anything more flexible (e.g., logos on images which have subsequently been resized) you're in to the territory of OCR and TinEye-like image matching, which are more advanced than I could advise you on.

To correctly detect all kinds of "tampering" and filter "illegitimate" from "legitimate" in general, you'd need an artificial intelligence that could understand the meaning and context of what it's seeing. The short answer is: you can't. That's what humans are for.

If this is for a website, probably the best thing you can do is a report button that lets users of your site report images that don't fit with your site's rules.