Hi tribalex,
I think you need to provide some more information here about how your content type is set up, and exactly what you are trying to achieve, because there are many ways to do what you are trying to do.
Here's one solution, assuming you want to store the "attribution" as an attribute of the <img> object in your HTML markup.
You will need 2 fields. 1 for uploading the image file, and 1 text field for storing the Attribution.
You can then apply the HTML typography plugin to your image field in your Content View (or Item View).
Click the +
Add this code: <img src="/$cck->getValue('name_of_image_field')" attribution="$cck->getValue('name_of_attribution_field')" />
Thanks,
James