使用PHP进行错误级别分析

Question

I am not a coder, but I do understand logic and usually I am able to do simple coding with PHP.

I'm looking to implement Error Level Analysis with PHP. You can see an example in this link.

Is it possible to implement ELA with ImageMagick or GD ? Any functions that I should look into it ?

Answer 1

This reference - http://www.errorlevelanalysis.com - seems to imply that you recompress a JPG image at some other compression amount (namely, 95%) and then do a pixel-by-pixel difference. You can do that in ImageMagick (or PHP Imagick).

For example in ImageMagick 6:

Input:

convert barn.jpg \( +clone -quality 95 \) -compose difference -composite -auto-level -gamma 1.5 barn_ela.png

I have stretched the result to full dynamic range using -auto-level and then did a non-linear gamma adjustment to enhance the differences.

See also https://sites.google.com/site/elsamuko/forensics/ela, where they provide two separate images and are looking for where they differ most as change detection.