Set of special test images :

aerial.bmp or aerial.pgm : grey 512x512

airfield.bmp or airfield.pgm : grey 512x512

airfield2.bmp or airfield2.pgm : grey 1024x1024

dollar.bmp or dollar.pgm : grey 512x512

finger.bmp or finger.pgm : grey 256x256

fingerprint.bmp or fingerprint.pgm : grey 256x256

moon.bmp or moon.ppm : color high resolution 1986x1986

testpat.bmp or testpat.pgm : grey 1024x1024