Capture regions of a pdf document and convert to image files - repost

Our business has field workers collect thirty-question free response forms from program participants at remote locations. Forms are standardized with identically-sized boxes (we will provide the form that is used and can modify it if necessary), and participants are identified by a sticker applied to the top of the sheet that contains a QR code that uniquely identifies the participant. We cannot expect that the stickers will be perfectly aligned, only that they will fall completely within a predefined region. We need a server-side solution that will allow field workers to upload pdfs of the answer sheets to our server and will then read the QR code and capture images of the thirty boxes and store them in a folder on our server with a unique name for each image. Our in-house programmers will handle all further processing from there. Because the pages will be scanned, the answer boxes will not be perfectly aligned in all cases, so the software will need to be able to find the answer boxes on the page and capture the full box (and ideally very little beyond the borders of the box). The software should be written in PHP if possible so our programmers can perform ongoing maintenance as we make changes to our form in the future. Attached is a copy of the form we are currently using.