Additional Information for each Image

i would like to add some more Informations to an uploaded image and not only title and an alternative text. I am thinking about some credentials, an subtitle or things like this.

I had a look at the code of imagefile and saw that this wouldn't be the problem by writing this right into the module. But i would like to write my own additional module and continue to use the upstream imagefile.module. Is there any hook where i can attach to for altering the widget and the processing of the widget?