OT: Any photographers/editors in the house?

Can anyone into photography recommend me any freeware batch editing software? I want to batch edit colours and levels on a load of pics but can't find any freeware aps. There's a plug-in for iphoto which cost 15 bucks which I dont mind paying but I downloaded the free trial and it says my trial has already ended. Confusing considering I've never used it before. I dont really want to pay for something I might not like working with plus on the website there's a lot of responses saying it's quite buggy.

There's other ones I've seen that cost like 40 bucks+ but fuck that, I'm not exactly a pro photographer so cant warrant spending that much. I got gimp which is a free photo editing software but so far cant find any batch editing options.

Can anyone help?

Cheers