I left work before I realized I left out the part about truth being Ms. Allen's burden because it is her
defense to defamation. (In US law, once the plaintiff has made a prima facie showing of their case, the burden shifts back to the defendant to prove their defense.)
Common elements of defamation in US law:
1) a false statement purporting to be fact concerning another person or entity;
2) publication or communication of that statement to a third person;
3) fault on the part of the person making the statement amounting to intent or at least negligence; and
4) some harm caused to the person or entity who is the subject of the statement.
Mr. Arrington has made a prima facie showing of the elements of defamation. (This doesn't mean that he's proven his case, since that is a factual determination by a judge or jury. It simply means that he appears to have shown sufficient evidence of each element that the factfinder could find for him.) I leave it to you to read the massive of wall of text to see how each element is met.
Truth is a defense to defamation, under American law. Thus, it is now Ms. Allen's job to prove the truth of the allegedly defamatory statements. In this regard, the photo is a significant obstacle to overcome in showing the truth of her statements, if, as suggested, she was several hundred miles away from the plaintiff at the time of the alleged incident.