How to compare 2 images from command line

[Andrew Gould]

On Tue, Sep 2, 2008 at 10:23 AM, FreeBSD <freebsd at optiksecurite.com> wrote:

> Tom Marchand a écrit :
>
>> Hash the images and compare the hashes.
>>
>>  -------------- Original message ----------------------
>> From: FreeBSD <freebsd at optiksecurite.com>
>>
>>> Hi everyone,
>>>
>>> I'm trying to determine if 2 jpeg images are identical. The images are
>>> screenshots taken with scrot at different times. The point is to know if the
>>> display is working correctly. I tried to use 'diff' but without success,
>>> probably because of the metadata included in the image. I also tried the
>>> 'compare' command from imagemagick, but it produce an image containing the
>>> difference between the 2 images instead of telling me if both images are
>>> identical.
>>>
>>> So, my question is what are you using to determine if 2 images are
>>> identical?
>>>
>>> I'm using FreeBSD 7.0 and I need to be able to script this comparaison
>>> for an integration in Nagios.
>>>
>>> Thank you,
>>>
>>> Martin
>>>
>>
> I just tried it and it doesn't work. The hashes are different. I can't
> say that I'm surprised since 'diff' is "seeing" a difference between the
> two identical images.
>
>
> Thanks for the suggestion
>

Yes, there's a huge difference between testing differences in images and
testing differences in files.  What do you mean by "...know if the display
is working correctly."?

Andrew