You can easily create a proof directly from a Trello card attachment. Just follow these steps:
Open the Trello card that has an attachment. On the right panel, select the PageProof Power-Up, then create proof from attachment.
Choose the file attachment you want to proof in PageProof.
In the proof set-up screen, create and send out the proof.
Note: You’ll notice that the proof is already referencing the Trello card automatically.