Chances are photo and video backup for Windows Phone 8 wasn’t available for you if you’ve lived outside of the U.S., and other officially supported countries. That has, as of now, changed, thanks to Microsoft and the company’s announcement to flip the switch on the feature around the world.
The ability to back up full-sized photos and videos is being rolled out worldwide but it might take a little time until you’re able to use the feature. However, when it reaches you, you can enable it by going to SkyDrive within the Settings of Photos. There you will have the option to upload good and best quality copies of your photographs and videos. While you will be able to duplicate your content via Cellular and WiFi for good quality, you’ll be limited to WiFi (for obvious phone bill reasons) when selecting best quality.
Since this photo and video backup for Windows Phone 8 update is a backend feature, there will be no need for you to do anything on your phone. The options will appear once the feature reaches you (and according to reports Australia already has it).
Source: Windows Phone Blog