ta věc má dokonce help:

•Previous (the Backspace key): open the previous image file,
•Next (the Space key): open the next image file,
•Previous Selected (the Ctrl+Backspace key): open the previous selected image file,
•Next Selected (the Ctrl+Space key): open the next selected image file,
•First (the Shift+Backspace key): open the first image file,
•Last (the Shift+Space key): open the last image file.