CMM2 supports some common image formats: BMP, GIF, JPG and PNG.
Font format
There's an overview in Embedded Fonts.pdf (where to get this?)
UTFT standard (see http://www.rinkydinkelectronics.com for the details)
Sprite graphics can be created by sampling from the screen, or with sprite graphics files in PNG or extended CMM sprite format.
CMM sprite format: The CMM2 supports creating sprites by reading in an ascii file formatted as described in the Colour Maximite manual with a key enhancement: CMM2 sprites can be any width and any height
This manual includes a description of the older version of the format: https://geoffg.net/Downloads/Maximite/MMBasic%20Language%20Manual.pdf