I would be interested in an addon that would allow administrators to attach an image file to the invoice/ job number. A file that could be attached and sent separately from the invoice or quote, as an additional follow up email which is attached to the same job/ invoice number.
If you can visualize… on the backend interface, in the quotes area, next to the send email and pdf buttons in the upper right side, there could be a third button that would ask you to choose an image and a “send attachment” email. The system would then email the customer a link, just like as a quote or invoice, only it displays the image asking for an approval or reject.
The system would then display a status ont he backend list of invoices, next to the order status, weather it was approved or rejected. If its rejected the admin would just keep resending, same process, until it was approved.
Additionally, It could be used to attach other documents and contracts as well. If done right, you could add your own HTML containing whatever shortcode and other forms that may already be accessible on your site and or anything that needs customer approval or feedback .