Let's Plays of the Danganronpa games have been an incredibly valuable source of screenshots that would otherwise be very hard to find, e.g. game locations without characters present. Thanks in particular to FPzero for his screenshot Let's Plays of Danganronpa: Trigger Happy Havoc and Danganronpa 2, and to Solitair for Let's Playing Danganronpa V3.
The Danganronpa Wiki and Fanganronpa Wiki have also been a useful source of images!
The picture of beta Fukawa is from Reddit user kahootmusicfor10hour, who's also posted other beta designs from the first game here.
Other screenshots were taken by the Steam community. Thanks to the Steam users DriveLove, Sin and Z0mb1eH3r0.