SouthAmericaLiving - 1:10 pm on Sep 10, 2011 (gmt 0)
If you use a copied image on your site, you should be honest and provide a link to the page you copied it from, even if it's in the public domain.
(was offline, sorry for late reply) I always attribute images, as a professional writer you won't find me copying anything... but don't agree with the above as is not necessary for these images, they are free use and for most of them you can't even find the actual photographers name for credit, they have a log-in name as attribute (their Google account).
I didn't think about being flagged as a 'Wikipedia content user', that's a good point but due to the amount of content on Wiki and extent of topics covered I'd think Google would have an incredibly difficult time making any connection between the info on Wiki and info on a site who may have used some in writing an article (not talking copying here, but as a source).
Google has a problem identifying duplicate content and not penalizing the original creator of the work (though of course the first article published is the original) from what I've read here, so not sure how effective they would be in trying to penalize folks who use Wiki as a source at times... or why they would even try. Duplicate content, copying Wiki content of course... even though it may be allowed by Wiki's Creative Commons ShareAlike License as long as is attributed.
This may be similar to many issues of a 'percentage' potential problem. If all images on a site were Wiki images Google would have motivation to penalize in support of those who create unique works but hopefully using a few doesn't mark you in any way.
I replace Wiki images when I can (travel to an area and take my own or use other original images).