Gpicview is just an image viewer, always has been and probably always will be. Beats me why it is included in so many distros by default. There are numerous other lightweight image viewers available which offer simple editing tools like cropping. My favorite is Mirage: http://mirageiv.sourceforge.net/
Mirage offers cropping, resizing, rotating, slide-show tool, renaming, deleting and a saturation adjustment tool, besides a super viewing mode.