Open the background tab. Menu → Import and Export → Import Background Image (Ctrl-B or Command-B)

Click on “Add” under Images in the tool box.

Select an image.

Select the first tool in the tool box.

Create a rectangle around the letter you want to import.

Click on the rectangle.

Click on Select Glyph under Parts in order to send the background image to a glyph. Click on Unicode if you get the message “No glyphs in this view”.

You can also insert images directly from the editing view: