Image size in posts limit

[Overread]

I know we already have the image resizer in posts - but is there a way to prevent posts being made if images linked to them are larger than a fixed size?
I ask this as we have had a few people recently, beginners, who are starting off by uploading fullsized images (3000+ pixels on longest side) which even if your on a broadband connection can take a long time to load.
If the post could be stopped before its posted and a note/warning given to the poster to tell them to either resize or link direct to the image that would help things out (note that means the code would have to tell the difference between an image in