I realize that it is impractical to think you can get higher quality out of a already blurry image. That's like trying to make 12 twelve loaves of bread from 2. However, I was wondering, say someone had put a blur effect on an image and you happen to know the algorithm used to create the blur effect. Could you, knowing how it was blurred, inverse the blur to get the original unblurred image?
It's possible to some extent. It's called image restoration or signal deconvolution and there are lots of research on this field.
Here's a nice presentation.