slackbuilds_ponce/desktop/pspshrink

pspshrink (ISO compressor for PSP games).

pspshrink it's a GUI for convert PSP game images into a .cso format, it allows you 
to shrink your isos to the cso format which is compatible with Devhook.

An alternative to pspshrink is "ciso", a command-line tool also available on SlackBuilds.