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First, I have to wonder why you would want to be in the server business. There are so many technical issues to keep up with and so many companies do it so much better than you can for so much less.
Anyway, I've posted a few pictures at Flickr over the years, but I never much cared for them as a host. With their recent "redesign," I pulled all my pictures because I think it's abominably inept. They apparently designed it for portable devices, and on a conventional computer, it's just a jumble. I used to be able to see pictures posted by my contacts at a glance; now I can't even find them. I liken it to somebody just taking a thousand snapshots and tossing them in a shoebox -- good luck finding anything. I still go to Flickr, but only for the groups. I think their groups are a strong point, and they have a group specific to anything you can imagine. Want a group to see pictures of snakes making love with bicycle tires? They probably have one. It's good if you have a particular interest, ferries, abandoned buildings, boxcar graffiti, etc. Also good if you're evaluating a possible purchase as you can look at groups for that item and see images and discuss performance with users of that product.
For several years now, I've used Smugmug to host all my pictures. It provides another backup as well as having a variety of display options. You can customize it any way you like -- and I'd have to think there would be nothing you could do with your own server that you can't make happen at Smugmug. They are also set up for sales and printing. Last I heard they were using Bay Photo for a print producer. My only niggle with them is they sometimes seem a bit childish, but that's reflective of an overall cultural deficiency I suppose.
I briefly tried Ipernity. They are structured a lot like the old Flickr, but I found a dearth of groups and overall it just had a creepy feeling to it.
Lately I've posted some to 500px, but there seem to be no groups. They have a "story" feature I would like -- you can use your images to illustrate a story you want to tell, but it is almost impossible to find the stories section (no link I can find) so I can't imagine you'd have many people reading your stuff. People seem to comment on photos there more as a way of getting you to look at theirs than anything. Their display is good, and if you just want to share with friends through links, that's probably a good way to go. I don't know about sales or printing through them.
As for security, I think if someone wants an image and has the capability it can be stolen. You do what you can, but there are no real assurances of safety in that regard.
