Every once in a while, someone needs a picture of me looking all serious and scientific and geologist-y.
I have exactly zero pictures of myself looking not ridiculous while doing science. Either it's -30 degrees out and I'm wearing a million layers and all you can see is my nose sticking out of an oversized hat, or I'm grimacing because something else is going wrong or I'm not wearing the right safety gear (hey, I have a small head and safety glasses fall off my nose in about 15 seconds if I bend over to do something).
Also, I am a big fan of documenting everything when I'm in the field, and nobody else I work with seems to have the same compunction. I end up with sole custody of the project camera. So I have lots of field pictures of other people.
One of these days, I'm going to find myself in an interesting place, and I'm simply going to hand the camera to a coworker/contractor/client and pose. And then I'll have one good picture I'll use for everything.