Set of old classic test images :

bridge.bmp or bridge.pgm : grey 512x512

cameraman.bmp or cameraman.pgm : grey 256x256

couple.bmp or couple.pgm : grey 512x512

clown.bmp or clown.pgm : grey 512x512

crowd.bmp or crowd.pgm : grey 512x512

girlface.bmp or girlface.pgm : grey 512x512

man.bmp or man.pgm : grey 1024x1024

sailboat.bmp or sailboat.ppm : color 512x512

tank.bmp or tank.pgm : grey 512x512

tank2.bmp or tank2.pgm : grey 512x512

truck.bmp or truck.pgm : grey 512x512

trucks.bmp or trucks.pgm : grey 512x512

zelda.bmp or zelda.pgm : grey 512x512

zelda2.bmp or zelda2.pgm : grey 720x576

ZeldaColor.bmp or zelda.ppm : color 787x576