What the "atom:image" element describes is a logo for the feed--let's call it "atom:logo".
Calling this element "image" provides no benefits over calling it "logo", but does have potential drawbacks:
Section 4.2.8 of draft-ietf-atompub-format-08.txt states:
The "atom:image" element's content is an IRI reference [RFC3987] which identifies an image which provides visual identification for a feed.
The word "logo" more precisely matches this description than the more general term "image".
Using the name "image" could lead to confusion if an extension element is introduced for, for example, associating an image with an entry.
Change the name of the "atom:image" element to "atom:logo".