I have always felt if you are concerned about your images don't post them, but when you put things across the image (easilt removed with
PS) or make them so small or such bad resolution they cahn't be seen properly, then why even bother.
If you have a great images you can watermark it and make it traceable, then can in a second find out anybody that has used it and go after them for copyright infringement.
As student you can use work you get off the web for instructional; purposes, and I as many other students do that.
Often times when I find a neat image I want to fool around with I email the person and ask permission, explaining I am a student and will not be gaining any monetary compensation for the image,
I have never been denied permission to use somebodys photo.