I would suggest that simply removing it will not suffice for repeat-offenders. Perhaps a 2-strike policy should be put in place. Do it once, you get a warning and have it removed, do it twice and you're account is banned?
I think copyright infringements should be taken very seriously, even if it's using an icon from someone elses style on your site (without permission).
Also I think it's important for users to clarify *if* they have been granted permission to use someone else's work on whatever graphic they have posted, to prevent confusion