Capture Attachment IDs

In my custom theme, I’m using a user_register hook to do some additional processing of the form contents after submission. For almost every entry, I can grab the necessary information straight from $_POST, but for image uploads I’m really interested in the attachment ID assigned to the image when RegistrationMagic adds it to the library. Is that information externally accessible at that stage?

https://wordpress.org/plugins/custom-registration-form-builder-with-submission-manager/