Adding watermark on pictures on submit

We have a website and we want to generate a stamp with the logo of the website and the username of the member on a specific font (already on the server). Here's the to-do list : 1) Generate the stamp on registration (logo + text, text = username). One black and one white (same template/size/etc). We already have the logo. 2) Print the stamp/watermark on a preselectionned $_FILE 3) Send it on our amazon S3 bucket (already done this part) If you work well. We can have a long term outsourcing relation.