You don't even need threads, you can load the images in a idle callback.

Here is an example I've made some time ago. It's a much more complex example, because it doesn't use a IconView, and it's not very clean, as the code comes from a much bigger program and I just made some quick modifications to make it work by itself, but it works very nicely.

To use it, pass it a list of files in standard input, for example with find :

find ~/Pictures/ -iname \*.jpg | perl mosaic_standalone.pl

It is made to display HUGE list of pictures, that's one of the reason it doesn't use Gtk2::IconView. But the principle of loading the pictures in a idle callback can be used with Gtk2::IconView.

You can find it here