System is saving images even if it cannot post them

[kingthrillgore]

Steps to produce

1. Add image to imageboard via file browse
2. Submit w/o defining any field content
3. "Horrible Form Errors" message appears
4. When attempting to reupload image with same checksum, it reports that a duplicate exists.

[kingthrillgore]

Interim assigned to @mrdaemon but not opposed to fixing this myself