Forum:Preload image description when uploading

Hello, I know the code to preload a default text when someone uses Special:Upload, it's something like: but this will preloaded even when an already existing image is being updated. Is there a way to avoid this? When someone upload a new version the link has, can be used in the if condition? For example something like  will work?

I think I found the code I wanted: If you like it, copy it.