I want to couple a comment and an attachment, but it seems that attachments exist separately from comments. I want to make a feature request, but before I do, I'd like to make sure it's not possible.

I use Trello in my research, almost as a lab notebook. I have comments about my progress on a task, and frequently I also include plots as image attachments. I'd like to add a comment specific to the image, and usually I have to do this subsequently as a separate comment: "The plot attached below shows ...".

Is there a way to add a comment to an attachment?

No, there isn't currently a way to add an attachment to a comment.

Comment Referenced Attachments Markdown-powered Workaround

Per @bobby-grace, not currently supported.

I work around this with card attachments + Markdown.

For example, I upload an image.jpg to my card which I'd like to reference in a comment:

1. Upload image.jpg to Trello card.
3. Make use of the GitHub-flavored markdown "linking" syntax in your comment. Paste that link between the [ square brackets ] like so:
here's that [image.jpg](https://trello-attachments.s3.amazonaws.com/589f2f4cbcfb178dd45a1c2a/58a8573c44ecd49c277cade6/f4c6d9f67dd479d5821a5f2e3784e7dd/upload_2_26_2017_at_2_15_05_PM.png)