It's almost random, but most of the time, if I swipe from right to left on the touchpad of my keyboard, it opens the photo search. I have not been able to locate any setting/tweak that explains this or would disable it.
I am guessing this was a problem with a k400 or k400r wireless keyboard (or some other logitech equivalent). If so I finally found and answer
Fn + Right Click -> Enables/Disables Gestures. Fn + Left Click -> Enables/Disables Tap to click.
Sorry for digging up such an old thread, but I have hit this question on AskUbuntu many times while trying to solve this problem over the years, so thought I would at east record the answer for myself.