Compare two images to determine degree of difference

[cssyphus]

I am using IrfanView in a custom Windows desktop app to grab a portion of the screen in order to monitor a condition in another program.

/capture=7=(-1830,40,100,40)

Until the condition changes, the screengrabs will be identical. I will make my app alert me when the two images are significantly different (say, 15% different) and when they are totally different (say 80% different).

Can IrfanView do this via a command-line switch (i.e. compare two images, report % difference)?

If not, does anyone know of another app that to do this via command-line switches?

Many thanks!

[cssyphus]

I solved this by:

In Irfanview, using the `/convert=...` CLI switch to also save each screenshot

eg:

i_view32 /capture=7=(-1830,40,100,40) /convert=c:\outfile1.jpg`

In DOS, using the built-in Windows/DOS command fc with the /B (binary compare) switch, and capturing the output

eg:

fc /B c:\outfile1.jpg c:\outfile2.jpg

Each iteration of the while loop, I delete one or the other file and re-run i_view's capture to that file, then re-compare. When "no differences found" is no longer in the output, I know the condition has changed.

The language I used to do this is WinBatch, a drastically undervalued IT tool that's been around since 1991.