How come whenever I put a picture on this site it looks blurry-ish and low quality but a lot of other people have amazing quality pictures? Does using 16:9 change anything?
If your photos look bad on GT5 then you may need to change your focus settings.
If your in the photo mode (the replay one) then make sure your shutter speeds are set up properly and your focus also compensates for a moving object!
If your in photo travel (the one for premium cars) then set your focus up right and if you want you can also change your resolution settings. This isn't the ratio but the amount of pixels the photo takes! Good luck.
If you're opening the image into Photoshop and re-saving, make sure these settings are maxed out. It could also be down to the hoster, as mentioned above. Imageshack is probably the better of all options for hosting.
Other than that, as also eluded too, the in-game camera settings make a difference. If the pictures look fine in the game, its likely down to the edit/host.