Just found this when searching for how to make custom cameras.... photomode, awesome! you can even change the time of day and position of the sun in photomode, regardless of the race time setting. Will have to play around with this and get some better screen shots!
To 'unlock' this you have to open
Program Files(x86)*\Steam\SteamApps\common\assettocorsa\system\cfg\assetto_corsa.cfg
(*or whereever your steam installation resides)
find the lines of code below and change the 0 to a 1.
Code:
[AC_APPS]
ENABLE_DEV_APPS=0
Then select photomode from ingame apps menu (RHS of screen with HUD element options).