1. Install the slackware binary package xfce4-screenshooter.
For the latest Slackware Linux release which as of time of writting is 13.37 xfce4-screenshooter-1.7.9-i486-3sl.txz can be download from here
Install of xfce4-screenshooter-1.7.9-i486-3sl.txz is done with slackware's usual installpkg package manager command:
bash-4.1# /sbin/installpkg xfce4-screenshooter-1.7.9-i486-3sl.txz
By the way, I haven't used slackware for a long time so in the mean time since Slackware 13, the default slackware packages format .tgz is now substituted with the newer .txz (better compressed .txz). The old .tgz was simply a tar archive with DEFLATE gzip. The newer .txz packages bundled with newer slackware releases are using the LZMA2 (XZ) chain algorithm for compression. LZMA implies higher compression than even bzip2 and this is the reason why Patrick Volkerding – the one man army man behind Slackware decided to use it.
The reason Vollerding choose using .txz is slackware network distribution will load up less the networks and will take less time for downloading extra slackware packages via the internet. The .txz also reduces slackware main CD size so more packages can be contained in the same 700MB sized slack install CD.
Anyways now back to the installation of xfce-screenshooter.
Once installed to runit use the Xfce menus:
Xfce Menu -> Accesories -> Screenshot
Next you will see the xfce-screenshooter program to pop-up:
To take a snapshot of the screen use:
Entire Screen -> Save