I would like users to be able to attach an image to the registration.
Right now the Registration needs to be approved by the admin - is it possible to include an image in this email so that a user can attach work that they have already done?
No. Such a feature doesn't exist (and I can't see the point in it). If you need that feature, you'll have to write the code for it I'm afraid. However, instead of registration approval by the admin I suggested implementing upload approval for the registered group. If users have proven that they are worthy, promote them to a group that has upload approval disabled.