Each year as an introduction to portraiture using a grid method, I have my Art students enlarge and draw what appears to be a totally non-objective image. I give them a small square with the image on it, and they draw it onto a larger square.
They don't know what they're drawing until all of the squares are put together to form a picture!
Intro to this exercise involves doing value scales and also doing some preliminary drawings that simply involve copying various shapes.
They are given 1/2" squares of a Photoshop-altered photograph and enlarge the images onto 2" squares of white paper.
All squares are coded, and when students complete the 2" squares, they glue them onto a large sheet of paper, to form a large, mosaic-like portrait.