My two cents on this...
If the author of the image does not want it to be use, copyrighted or not, it should clearly state it. Most copyrighted images have a watermark to distinguish them. Others just can't be copied by browser blockage.
There are a number of free images services, some require subscription others don't.
Douglas has recently posted a like to a royalty free repository, with thousands of image in very good quality.
Bottom line is, for me, unless it's a brand image, or it is clearly stated as copyrighted, its free to use.
Legally, compared, its the same as me putting my brand new TV outside unattended for a couple of hours, I should not expect to find it standing in the same place waiting for me. No judge will grant me prejudice in that scenario.