Hello, Elena!
Comments allow you to engage in a conversation on the back of a card. To view the back of a card, click on the card to open it.
You can add comments to a card via the "Write a comment" text box in the "Activity" section of the card back.
When you comment on a card that you're not already a member of, you can Watch that card to help keep up with any replies that come in that don't mention you. To do so, you’ll need to check the “Watch” box.
https://support.atlassian.com/trello/docs/commenting-on-cards/
If I understood your request correctly, the best option is to upload a single media per card on the list. This would make it easier to check every comment that is made but I noticed that if you use the comment button, it will attach the answer to the link of the uploaded media as well.
I hope this helps, but please let me know how it goes and if there's anything else I can assist you with. Looking forward to hearing from you!
Kind regards,
Alisson
Trello Team
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