If I recall correctly Robert Vonk of Fotohuis used to sell a thing called a Versamask which was a metal easel with very accurate metal masks for 6x4, 5x7 10x8 etc which gave a penline as thin a 1mm on the edge of the print. Not cheap however.
It looked a very easy and convenient way of doing it without any skill required. Such easy and convenient ways always come at a price - usually quite a large one.
Someone with access to a laser cutter, even one only able to do plastic such as schools have could create such an easel or easels