Is there a way to allow users to upload photos to my website for public viewing, such as the photo sharing sites do? For example, i'm building a site for a tennis organization and want members to be able to post their photos on the site.

I use Piwigo.
You could use the new form builder for them to submit their photos. Depends on the level of control you want and how much interaction you want to have with the submissions.

What about Sdrive Stream, if you don't mind them loaded 1 above the other ?

Just have to either limit the number of people who can send them, or set up an alias email address, so everyone sends pictures from 1 email address, from either their pc or mobile device, could be handy as instant !