I recently bought an iPad 2 for my parents, and I'm looking for an app that allows me to share photos (JPEGs) on my Windows PC with them. I imagine myself dropping the images somwhere, and they can see the photos by opening the app. I would like something simple to use that doesn't require sending a link or opening a browser, and that the pictures be private. I would also accept an app that only stores pictures temporarily (they are not meant for long-term storage).
The easiest solution I can think of is Dropbox: You can just drop (as the name suggest) some photos in a folder on your PC or Mac (or another mobile device) and they'll automatically be synchronized with the folders and apps on your other devices.