Clean up validation errors from a_a_a?

Currently i get the following errors from validation, if entering
nothing in my add image form. The items noted with the > are those from
my own validation. I expect and want to keep these. What i would like is
to remove the following, as they have nothing to do with the user:

  • Content type can’t be blank
  • Size can’t be blank

And if possible clean up the following:

  • Content type is not included in the list
    replace with : File is not an image
*Size is not included in the list
         replace with : image size is too large/small

7 errors prohibited this part from being saved

There were problems with the following fields:

* Content type is not included in the list
* Content type can't be blank
> Name required
* Size is not included in the list
* Size can't be blank
> Catalogue number required
> Filename can't be blank