Use avatar from file or url

[eluser]Sein Kraft[/eluser]
Not...I'm asking how detect and use a simple avatar uploader.

In the form the user has a file input and an common input text. I need to check if the user has uploaded a file or if the user has ussed the other input to set an external url for the avatar.

Thats my question. And yes, I use a table to save the ur of the users avatar, thas not the problem.