Canon PIXMA MP800R Quick Start Manual page 28

(3) Close the film holder.
(4) With the front side of the film (the side showing
the correct image) face down, set the film
guide on the Platen Glass and align it with the
indentation on the left.
Mounting 35 mm Slides:
(1) Align the film guide with the indentation on the
left side of the Platen Glass.
(2) Mount the slides in the film guide with the front
side (the side showing the correct image) face
down, and with the image upside down. Load
the slides in the landscape orientation, making
sure they are not loose in the film guide.
Photo Printing from Photo or Film 27