How to compare 2 images from command line

FreeBSD freebsd at
Tue Sep 2 16:22:05 UTC 2008

andrew clarke a écrit :
> On Tue 2008-09-02 11:57:35 UTC-0400, FreeBSD (freebsd at wrote:
>>> Can you put the screenshots into some other format?  As you mentioned,
>>> the jpeg format includes metadata, which might include the creation
>>> time and would cause every image to be unique from a filesystem view.
>>> For example, I don't believe bitmaps include metadata, which would cause
>>> them to be identical if the display were identical.
>> Thank you! It did the trick. I just converted the image from png (sorry  
>> it wasn't jpeg...) to bmp and it works with cmp. Even diff now recognize  
>> both images as identical.
> Before I read this I was going to suggest you could try removing the
> metadata using something like jhead.  As it turns out, you say you're
> using PNG format images, not JPEGs, but perhaps there's an equivalent
> to jhead to work with metadata in PNG files - just as an
> alternative to converting each PNG to BMP (which could be CPU intensive).
> Regards
> Andrew

Thank you for your "almost-suggestion" ;)

The screenshot are taken once every 5 minutes and the conversion was 
pretty instant. I don't think it will be a problem in our case.


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