1. A method of verifying a lithographic mask, the method comprising the steps of: providing a mask layout; providing a catastrophic error metric; providing a plurality of image models, wherein said plurality of image models is ranked according to relative accuracy; simulating an image for said mask layout using at least one of said plurality of image models; identifying a violation of said catastrophic error metric in said simulated image; identifying a portion of said mask layout corresponding to said simulated image that includes said violation; and simulating a next image for said portion of said mask layout using a next of said plurality of image models having greater accuracy than said at least one of said plurality of image models used in the prior step of simulating.