The Photo Stream is one of the coolest features of Apple's iCloud, allowing you to automatically share your photos between your iPhone and iPad. You can even get at the pictures from iPhoto on your Mac. But what about photos that you took before you enabled Photo Stream on your iPhone or iPad?
One feature that is missing-in-action on the iCloud is the ability to easily copy photos from your iPad's photo album or your iPhone's camera roll to your Photo Stream. While it would be nice if the share button would do this, there is no direct way to get your older photos onto Apple's Photo Stream. Luckily, it's rather easy to use a back door to accomplish this task.
The easiest way to copy photos to your Photo Stream is to simply email the photo to yourself. You don't even need two email accounts or even need to wait for the photo to arrive, just go into the Mail app and navigate to the sent folder of the account used to send the photo. To copy the photo to your Photo Stream, simply hold your finger down on the folder until you see the option to save the image. Once saved, it will save to both your photos section and your Photo Stream.
Note: Because we started by sending ourselves the photo, this means you will have two copies of the photo in your photos directory. Simply delete one of the duplicates when you are done.
Dropbox makes a good way to copy photos as well. If you use Dropbox, you can upload individual photos to your Dropbox folder within the Dropbox app and then save them back to your iPad. This is even easier than using email, but you will need to have a Dropbox account. (Don't worry, Dropbox has plenty of space available with their free account.)
You can also download the photos from Facebook, Flickr, etc. Any photo saved to your iPad will also show up in your Photo Stream, so if you have the photos on Facebook or Flicker, simply tap-and-hold the photo in the Safari browser until the option to save appears on the screen.