Before a sync or restore, I believe that iTunes will create a backup of your phone's contents (unless you manually cancel this backup). The backup will contain the photos and videos that were on the phone.
You can check if a backup was created by doing the following:
- Launch iTunes
- iTunes > Preferences > Devices
- See if there is an entry with the date of the restore.
If a backup exists, you can recover your data with one of two methods:
- Restore your phone using that backup; or
- Use an application such as iPhone Backup Extractor to extract the images out of the backup file.
Photostream will store the previous 30 days worth of photos automatically. That means, every photo you take on your iOS devices will be sent to Photostream, but only the last 30 days worth of photos will be available there.
If you enable 'Automatic Import' of Photostream in iPhoto (Preferences > Photostream > Automatic Import) then when you launch iPhoto, it will automatically download a copy of any photos that are in your Photostream, and automatically create an Event titled: {MMM YYYY} Photo Stream (eg. "Jul 2012 Photo Stream")
This Event will be automatically kept up to date, as long as iPhoto is open long enough to sync everything required (depends on your connection).
In effect, as long as you open iPhoto once every 30 days and leave it open long enough for your Photostream to be imported, you should never have to manually import a photo from your iOS device at all.
As for removing items from your Camera Roll on your iOS device, as long as you see that they are present in Photostream (or in iPhoto), then it is safe to delete them from your device. (There is no way around this but to do it manually as far as I know.)
Currently, Photostream does not support videos. To import videos, connect your iOS device to iPhoto and import these manually.
As a side note, in order to keep some photos on the device, you can create a smart album in iPhoto along the lines of "Photos taken within the last 30 days" or "Photos rated 4 stars or more", and configure iTunes to sync these to your device. That way, you can be sure that no matter if you clear your Camera Roll on your device, or delete certain photos, you maintain some convenience.
Best Answer
I don't know if this is an answer, but I wanted to add some images, so:
First, what computer / os do you use? Can you see the photos on this computer? If you are using iPhoto or Aperture and the photos you are looking for are not visible in these programs, they have already been removed from the iCloud server and cannot be re-synced to iPhone (at least not through Photo Stream). iCloud only stores the last 30 days worth, or 1000 photos, whichever limit is hit first.
On the iPhone, go to Settings then iCloud (as seen in the first image below). Next, tap on Photo Stream, and ensure the "My Photo Stream" slider is set to ON (as seen in the second image below).
Finally, (as this is iCloud (grrrh), it might help to turn these settings off, wait a few hours, and turn them on again. I had to do this recently, with photos and mail. Hope this helps.