This FAQ applies to Lumia phones with 256 RAM memory (Lumia 505, 510 and 610).
Windows Phone supports a user selectable option to automatically upload in the background pictures from the camera roll. To maintain good performance, this feature is disabled.
However, manual uploading is supported so you can continue to enjoy the service by manually uploading the images to the cloud. Go to Start > Pictures > Camera roll, tap the picture to open it, and then tap ... > Share on SkyDrive.