I do not know how to frame the question. And I do not know how the below tag is working...
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It sure does!
For example, take a look at this piece of software that is intended to dynamically resize an image.
http://imageresizing.net/docs/basics
If done correctly, adding parameters to an image url could be very useful.
Edit:
As others point out, you need to ensure that the server knows how to handle the extra parameter. In this case it is intended to resize/watermark/rotate an image. It can certainly do other wonderful things.