In either case, the background image must be saved in the PNG file format. Depending on the export page size, Arsenale suggests the following dimensions for the background image in order to render the export at a standard print resolution of 300 ppi. Note that Dataplane will automatically select the best page size to use based on the user's profile:
Letter (8.5 x 11)
A4 (210 mm x 297 mm)
If needed, the image you provide will be automatically stretched to fill the entire height of the page, and then the width will be scaled as needed to maintain the proper proportions. This means that horizontal cropping may sometimes occur if your image dimensions are not proportional to the selected page size.
If users will be exporting in both Letter and A4 sizes, Arsenale recommends using the A4 dimensions for your background image in order to avoid unnecessary horizontal cropping.