Image upload before checkout?

Hi,
New Zencart user, I am researching Zen capabilities for a business card printing client.
I need to ensure an image has been uploaded to the web server before going to checkout.
I was hoping to add another page between the cart and checkout that would perform the upload and do some checks. It the checks passed it would go to checkout, if they fail it would go back to the cart.

Has anyone done this or something similar?
Can it be done this way?
Any help pointing me in the right direction would be appreciated.

Thanks for any contribution

Ray

Images are uploaded by customers at the select-a-product stage, using the File Attribute function.

It can be configured to force an upload by making it a "required" option on a product's attribute selections. Customer cannot proceed to checkout until the required attribute is selected or condition is met.

Search the FAQ for "attributes", there is a tutorial there.

I set the attribute to required but I am still able to add the product to the shopping cart with out the user uploading an image. Any where else I should check for the required option?