Are there any sites that are like lang-8.com, but allow reviewing of hand-writing?
Is it socially acceptable to post hand-writing to lang-8 itself?
I don't think there is any site specifically tailored to reviewing handwriting. I think there would be no problem posting a picture of handwriting on lang-8, but you may get fewer corrections because it would be more annoying to correct. (This would be the case on any website of course, since it involves pictures to show the handwriting.)