From an open Cmap:
You can make an image appear in the background of a Cmap. To give a Cmap a background image, select Format, then Add... from the Background sub-menu.
The "Choose Background" window will open so that you may locate an image file. Click OK to place the selected image into the background of the active Cmap.
Now when viewing the Cmap, the background image selected appears as the Cmap's background.
You can make an image appear in the background of a concept. To give a concept a background image, select the concept, then select Styles... from the Format menu.
Open the "Styles" window to the Object tab. To continue adding an image to the background of a concept, click Select or Change Background. The "Choose Background" window will appear where you can browse for an image. Click OK from the "Choose Background" window to add the selected image to the background of a concept.
Now when viewing the Cmap, the background image selected will appear as the concept's background.