- Kallitype - obsolete printing process, resembling the platinum process. The image is formed in metallic silver rather than expensive platinum.
- Kerr cell - high speed shutter without moving parts, using two crossed polarizing filters at either end of a cylinder filled with nitrobenzine.
- Key light - studio light used to control the tonal level of the main area of the subject.
- Knifing - method of removing marks and other blemishes from the surface of a print by gentle scraping with the tip of a sharp knife.
- Kostinsky effect - development effect in which dense image points are inclined to move apart, relative to each other, and light image points to move together, relative to each other. This occurs because developer is not being equally distributed over the image point and is rapidly exhausted when to heavily exposed image points are close together.
- Kromskop - early viewing instrument invented by F.E. Ives, embodying a system of mirrors and color filters to synthesize a full color image. This enabled monochrome transparencies made from separation negatives to be rear-illuminated through blue, green and red filters, and then been seen combined in register as a single image.