Manipulating local files with JavaScript? I didn't looked thoroughly in Google for that topic but I think it shouldn't be possible, as it would be a biiiiiig security threat. If you could use it for resizing images, you could also use it to get access to data on client's computer. No, I don't think that's possible (and I'm glad it isn't 🙂 ).
I think that can be done with some ActiveX Control in IE, but then users have to trust your control and let it be installed first before using it.