The following is based on the Photoshop image editor although the principles should apply generally to other similar software.

To make the most economical use of photo inkjet paper the image has to be sized and suitably positioned on the background canvas.  The printer paper has to be selected to suit the canvas size and the orientation selected to portrait or landscape to suit.

Move the image on the canvas away from the leading printing edge by 0.5 cms to allow for printer top margin and to prevent part of the image from being cropped.  This may or may not be necessary depending on the printer.

Suggested Printing Sizes - Maximum Dimensions (Photoshop)