HP Deskjet 6840 Color Inkjet Printer - Manual (Page 139)

Printout has an unwanted border
For most photo paper types
If the printout has an unwanted border, then align the print cartridges .
For photo paper with a tear-off tab
If the border appears below the tear-off tab, then remove the tab.
If the border appears above the tear-off tab, then align the print cartridges .
HP Deskjet 6800 series printer User's Guide
139