Is it appropriate to use others' images in publications? I am writing a paper which will eventually include several of (my own) computer-generated illustrations.  However, I have found a similarly-styled image in another paper (not mine) which clearly and attractively explains a preliminary point that I am trying to make.  

Is it appropriate to use this image (with credit, of course) as an inset in my own paper?  I am genuinely not sure.  I have heard of people who avoid this practice so much that they will reproduce almost exactly the same image on their own, but I am not sure if this is strictly necessary.
You are writing a paper for publication: No

You are writing a paper for a class: Yes (If you cite appropriately)