Returns the user's profile image info
If the user exists and has a profile picture, the returned array will contain keys:
 f1          - the content of the default 100x100px image
 f1_mimetype - the mimetype of the f1 file
 f2          - the content of the 35x35px variant of the image
 f2_mimetype - the mimetype of the f2 file
The mimetype information was added in Moodle 2.0. In Moodle 1.x, images are always jpegs.