There two full-source examples in the package (static and client-side)
It looks like:
$cl = new imagecloud(800,600,200,200,255,3.27);
//init cloud (w=800, h=600, background color: rgb(200,200,255) and scale = 3.27)
//scale is important. try not to set it to large. 5 or max 10 is ok
$count = $cl->additem("items/image1.jpg",$value,$id);
//add item to cloud.
//value - weight of image. Must be [0-100]
//id - id of image.
//additem returns count of added images or "false" is cloud is full
//save item to file - save png file of image tag. with simple transparency.
//this function is used when you create client-side image clouds, so you need
//separate files of each tag
$array = $cl->getarray();
//get array of data. You will need this data to create cloud on client-side or to
//calculate id of image picked by user. So, you will need to save it. (see examples)
$im = $cl->create();
//generate image cloud. This will take some time
//and save it as image.
Examples will show you all. Check them