Stock photos are an incredibly lucrative but saturated market. Those that sucessfully sell rights to use stock photos are paid hundreds to thousands of dollars per photo (depending on usage). I've sold some stock photos to businesses as favors and have been paid pretty well for them. However, breaking into it is very difficult (I was only able to do it because i knew officers and or owners).
Photography is not something i've been able to quit my day job for unfortunately, but is a pretty fun way to make some good side income and definitely helps me justify my toy purchases
Stock photography is highly lucrative but has a ridiculously high barrier to entry, it is definitely a lot more time effecient that event photography. It's just way less fun.