Let’s see if this worked. If you don’t see a caption it worked:
Yep, it worked. I inserted the photo with an alt attribute but no caption. Turning off captions really should be a global option in WordPress rather than requiring theme hacking. An alt attribute is not the same thing as a caption, nor is the same text appropriate.
P.S. That’s a jumping spider that visited me at my desk for a few days, one of the Salticidae, the world’s largest family of spiders. Beyond that I haven’t yet ID’d it.