Related to T4863: Allow Workboard Cards to be customized for display, we've gotten requests from various designers, to enable an optional view that shows a "thumbnail of attachments" on the workboard cards. This would assist more visually-oriented people in finding/triaging tasks.
It's a core feature of Trello, as shown here:
For reference: The way Trello does it, is by giving users an option to "Make cover" or "Remove cover". I believe it makes the first attachment a "cover" image by default.
Then each board has a "Card Cover Images Enabled" setting.
Hope that helps. :-)