So true ... the Internet is truly "the world's largest copy machine!"
And, there is 'fair use', the guidelines for which do not include unauthorized posting of images on a website or other 'reproduction' without proper attribution.
There are some things artists and photographers can do, however, to stop would-be illegal users of our images in their tracks: include a watermark for one, and you should also change the DOCUMENT resolution (that is, the print output physical size - the
document resolution has nothing to do with the DISPLAY resolution, or web image screen size in pixels) to an ungodly number like 1200 PPI, for, say, a 650 pixel-wide web image. You do this in PS7 and PSE by
unchecking the "Resample" box before you change the resolution PPI figure within the
Document Size section of "Resize Image".
That way, upsampling is all they can do to your web-sourced image
for printing purposes, and the interpolation engines, such as "bicubic smoother", no matter how good, cannot get them a
print quality image out of it at any appreciable size.
Wade