In a recent talk I gave, I recommended using images to spice up your blog. I think it's great, and I often include images in my posts where I can. I typically grab screen shots, or use pictures I have, but I have linked from the Internet.
However someone asked me about copyright. My reply was that linking an image from another site should protect you from that. There was a case that went to through the courts that held a link, meaning a hot link (using the "img src=" tag), wasn't a copyright violation. But copying the file to your service and using it, was a violation.
However a few other people posted links to complaints people had made about hot linking, saying it was "bandwidth slurping or stealing."
I can see both points, and so I'm not sure what the proper thing to do is. I'll say this:
That's probably the best solution. I think that I'll give credit on future photographs that I use in my writings and copy them to my server.