Turn [IMG] to [URL] if over a certain size?

[ADM]

Theres alot of image resize scripts around but all I need is a hack to automatically make a link to the image if it's over a certain size.

I don't need it to resize the image or anything else fancy.

I want something that is quick for the user and not very server intensive.

Any help on this would be greatly appreciated!

EDIT: I originally posted this in the vB2 forum accidently so I've reposted it here and reported my other thread. Apologies.