Reblog = when you hit that little reblog arrow that posts a copy of the original post to your own blog with links back to me. I get notices when you do and when people reblog it from you and if anyone leaves additional comments.
Repost = when you download the image(s), either from tumblr or elsewhere, and then upload them in a fresh post. I get no notifications at all and it’s more difficult for people to find my blog should they have something to say about the art or want to see more.
I would never ask anyone not to reblog my art. You can do that all you want. That’s what tumblr’s built for and if I didn’t like it I would not be here.
However, reposting is rude as it removes the original creator from the process, credit or no. It’s also unnecessary in my case since all my art is already on tumblr.
I know a lot of people simply don’t understand the difference, or they think tumblr is like a photobucket where they can just upload anything they like. I never want anyone to feel discouraged for a simple mistake or misunderstanding. However, there are some people who do it just to get notes, or in malicious ways where they want to insult the art or take credit for it, so this is why I don’t allow it.