I recently had a need to take screenshots of webpages dynamically. What I came up with was a simple PHP cron and que that calls a very basic shell script.

!/bin/bash

export DISPLAY=\":1\" /usr/bin/opera -remote \"raise()\" /usr/bin/opera -remote \"openURL($1)\" & /bin/sleep $6 /usr/bin/import -window root -display :1 -resize $3x$4 -quality $5 \"$2\"

I then call this script with a command in php

screenshot.sh www.url.com /tmp/tempfile.jpg 1024x768 75 15

This will take a load www.url.com for 15 seconds and save a 1024x768px screenshot to /tmp/tempfile.jpg