The only reason I suggested daily is that someone new might be more inclined to visit daily rather than say weekly if there were a new photo each day.
If it were a weekly rotation the mentality might be more that they will stick their head in every week or so.
Quite a few sites have a similar insert at the top of the site page and these photos often get enough interest up for you to have a look at the thread it was from no matter how old the thread is.
Here is one site I frequent for the kitchen side of things but those photos have sucked me into delving deeper many a time.http://somersoft.com/forums/
daily might get a little more action happening on the forum ,
and then it might not!
I want to stand as close to the edge as I can without going over. Out on the edge you see all the kinds of things you can't see from the center.