Assuming the images are posts. Register a new post meta for them and use the ID for your form in that post meta, this will allow you to relate to the form.
https://codex.wordpress.org/Function_Reference/add_post_meta
Assuming the images are posts. Register a new post meta for them and use the ID for your form in that post meta, this will allow you to relate to the form.
https://codex.wordpress.org/Function_Reference/add_post_meta