snapshot and waterfall images

I have a local instance installed on ubuntu 10.04. I have apache php and ffmpeg all installed and webpagetest runs, however for some reason i am having difficulty getting the waterfall and snapshot images to show after the application runs. What could be the reasoning behind this, the only thing I can thin of is if ffmpeg is incorrectly installed.

sudo apt-get install php5-gd

ffmpeg is just used for the video static images. The GD library for php is probably missing (used for drawing the waterfalls and generating thumbnail images).

You may also need to restart apache after installing it.

Excellent, worked like a charm, thanks.