This is a slighly modified version of an old GIMP Lomo plugin I’ve used for ages that will now work with the new GIMP 2.4 release thanks to some advice I remembered reading on the GIMP User mailing list. The original plugin is by Francois Le Lay but hasn’t been updated since 2005. It’s a basic script but it’s very effective. Just be warned, if you resize your image, make sure you right click on the Vignette layer and click “Layer to image size” before the resize. Otherwise odd things happen!
Download
Download gimplomo.scm.
Install
Installation is easy. Simply copy gimplomo.scm into your .gimp-2.4/scripts/ folder and restart the GIMP. It will appear as Image->Filters->Light and Shadow->Lomo.
Example Images
Below are two before and after examples of what the Lomo plugin does to images. I have also posted fake lomo photos in the past which should give a really good idea of what it’s capable of.

Before and After Lomo images
Why the change to Script-fu?
Script-fu in GIMP 2.4 requires that variables be defined before using them which has broken a lot of Script-fu scripts unfortunately. In theory it’s a great change because it tightens up on sloppy programming but it hurts the end user!