A new 'Photo Mode' has been intoduced for GT4 at this year's E3. This mode will allow players to set up a photoshoot in their choice of several different loactions or on any of the multiple tracks available in the game. This new mode will simulate the locations and cars with photorealistic quality and will generate a mega-pixel sized digital image, to be printed on a USB photo printer. Additionally, these photos may be able to be moved onto a computer system; this is something that is currently being considered.
For sharing your pictures with other GT4 players, the image stores all of the vital information that comprises the picture and this stored format (not rendered) is a small format that can be shared with friends, allowing them to render it on their PS2s.
Part of the reason this matters at all is that the spectators are no longer flat, but are fully 3D models that look quite realistic.
I know it sounds like this is a 'Pokemon Snap' feature being added, but those who love automobiles and photography may find themselves quite fond of this new mode.