How to compare 2 images from command line

[FreeBSD]

Polytropon a écrit :
> On Tue, 02 Sep 2008 11:31:49 -0400, FreeBSD <freebsd at optiksecurite.com> wrote:
>> I want to determine if Mplayer is working correctly. The best way to be 
>> sure is to check if the display on the screen is changing. That's the 
>> purpose of the screenshots.
> 
> And this works? I always thought mplayer would output the video
> stream via DRI / DRM, so on the screenshot, nothing would be seen...
> 

Yes it works. I don't know how scrot takes it's screenshot but it does 
it well ;)

>> The screenshots are taken by Nagios every 5 
>> minutes and the new screenshot is compared with the preceding one. But, 
>> by now, it doesn't work because every tool we try is seeing a diffence 
>> between 2 identical images.
> 
> The images may be identical in content, but it's completely possible
> that other data (others than the pictural information) is coded into
> the file, for example date and time of creation, so the files may be
> different, while the pictures they show are identical.
> 
> It would be useful first to "decompile" the files - create a new file
> that only contains pictural information, nothing more.
> 
> 
>