I was getting up from the bed, he was throwing the stuff off the dresser onto the floor (cleaning everything off the dresser) and when I sat up, a picture frame hit me and cut my face. So I went to the hospital to have it stitched up so that it wouldn't leave an ugly scar.
Okay, can I assume that this is what happened?
You go to the hospital (did BF even go with you??). Doctor asks you what happened, looks at your face. Doctor calls the police and reports to them the possibility of abuse (which they HAVE to do if it's suspected). BF gets arrested for DV.
Is that it in a nutshell? If so, I have to say that I've known many, many, many an ER doctor and they rarely ever assume abuse without reason. Chances are, if an ER doctor thought your injury was a result of abuse, a court will, too.
Now, it's quite possible that you, sitting there as a witness, will be able to make a case for your BF's innocence in the matter, but as others have said, you'll be met with considerable incredulity considering how many abuse victims recant later.
I do hope, that if it IS truly "just an accident" that the truth will out ... however, I really think that you're sugar-coating things ... as someone else said, the glass found in picture frames doesn't break easily. It had to involve quite a bit of force for it to break on encountering your cheek.