be of image type IMAGE-TYPE if IMAGE-TYPE is a symbol. If not a symbol,
IMAGE-TYPE must be a pair (PREDICATE . TYPE). PREDICATE is called
with one argument, a string containing the image data. If PREDICATE returns
be of image type IMAGE-TYPE if IMAGE-TYPE is a symbol. If not a symbol,
IMAGE-TYPE must be a pair (PREDICATE . TYPE). PREDICATE is called
with one argument, a string containing the image data. If PREDICATE returns