Thanks for the response.
The reason I was asking is that my mother is retired so she's on a fixed income and she tries to avoid as many subscriptions as possible. It peeves me that the only way for her to view her photos from her computer on her Apple TV is to have a subscription to iCloud (or Flickr). It's especially annoying considering she used to have 30GB of storage on her first-gen Apple TV (which was entirely used for photos). Now she can spend $40/year for 20GB or $100/year for 55GB. And again, all she wants to do is make a slideshow to show her friends photos from her last vacation**. She doesn't want to do this stuff on the road, just in her own house. She shouldn't have to pay for this. This is bogus.
But thanks for your response, Andy. I guess I was just hoping for better news

3. Or an iOS device, you delete photos from the stream in iOS. I don't think you can do that on Apple TV
By manage I include "get on-to." I see no way to get photos from her computer onto Photo Stream, and it seems the only way to do it is through iPhoto.
Does iPhoto manage the placement of the files for you, or are you able to put them anywhere? My mother likes to create folders in which to put her files, with a specific naming convention. She wouldn't like to do the placement through iPhoto. Picasa just displays the photos and doesn't automatically do any file management. Is iPhoto the same?
**before you say it, I know you can fit a vacation's-worth of photos on the free 5GB, but what won't fit is the decades-worth of photos she likes to see on the Apple TV screensaver...