Maybe the pictures are not compatible with your iphone 4. Try this maybe it will help. Connect your iphone 4s the if your using windows go to computer then double click the apple iphone then internal storage, then dcim and click the folder after it. There you will see the picture files. After that copy it to your computer but remeber to paste it in a folder. Then disconnect your iphone 4s then connect your iphone 4 by using the sync pictures tab in itunes. Choose the folder that has the pictures on it. then press apply.
If you still have your iPhone 4S, back it up again and try restoring to the new backup. If that fails, connect the 4S to your computer and import the photos to your computer (see http://support.apple.com/kb/HT4083). If you don't have the 4S anymore and restoring to its backup isn't working about all you can do is use 3rd party software such as iPhone Backup Extractor to see if you can successfully extract the pictures from your 4S backup. (This won't be successful of course if the backup itself contains corrupted photos.)