Create image processing php script in Magento shop

I have a laser engraving business, and would like to generate a simulated preview of engraved products using user-uploaded designs. I need a function written and integrated into my Magento shop which will do the following: 1. Allow user to upload image ("User image") 2. Resize image to match a predefined size 3. Convert to 1-bit black and white 4. Create a final output image using "user image" and 2 pre-existing images ("A" and "B") as follows: Areas which correspond to the black areas of the processed User Image will be taken from "A". Areas which correspond to the white areas of the processed User Image will be taken from "B". The function should be written to accept basic image types (jpg, gif, tiff, png) and reject others. It should reject files above a threshold filesize. The User Image needs to be available to store admins, and somehow referenced to the user's order.