I am/was in the same situation as far as popularity goes with my desktop application (for OSX), and I personally went the route of not monetizing at all. To me,

I am/was in the same situation as far as popularity goes with my desktop application (for OSX), and I personally went the route of not monetizing at all. To me, the knowledge gained through every feature I added and every bug I fixed is/was more valuable than the money I could have made. Then again, I have a great paying job that I love, and I primarily built it because I couldn't find a similar application with the features I was looking for, so other people finding it useful is just a bonus. Plus, it's a great way to show that I have passion for development outside of work, and that I'm continually trying to improve myself as a programmer/engineer. I even provided detailed Arch/Design/Req docs in the github repos, just in case anyone was interested in looking. Of the options listed in this thread, I like the idea of adding an "in-app" purchase for the feature you mention gets requested a lot (photo uploads I believe). The knowledge that will give you is immensely valuable (being able to turn features on/off in the same application), if you don't already have that built in. Anyway, that's just my opinion, but you should do whatever you think will make you happy.