Andem - 8:15 pm on Sep 5, 2012 (gmt 0)
There is a thing called Fair Use
I don't want to nitpick and I agree with your point of view, but using high resolution images without permission from the copyright holder is infringement.
Wikipedia's usage of copyrighted photos is within fair use (ie. 250x250px). Google's usage of thumbnails in image search results might also be fair use. An 800x600px photo does not fall under fair use.
When the originator of an image is no longer profiting [as much] from their works because somebody else has infringed upon his/her intellectual property, then it may be viewed as a form of theft.