gui? maybe you should be familiar with it by some manual.
It is so convenient to control and edit the image file but most of them are hot key mode.
For example, you wanna see all of the pictures in your image directory:
and then press "space" will be next. Also the key "<"(means "Shift+," in your keyboard) would magnify the image and ">" is the opposition. And the command "convert" still have many functions.
Check the manual from the official web site of Imagemagick then you will get more useful things.