31 or 13?

 

Original: Jack's hair is receding and cut in a way that looks like a backwards "3." The single strand that falls on his forehead looks like a "1."  

Photo reverse: the "1" precedes the "3," spelling "13." 

If you're not convinced, at least consider that the "1" strand in the original photo (top) seems to split off an pointed piece of Jack's upper left forehead, giving the appearance of devil's/bulls horns.