If you upload an image, the URL field is populated with the URL of the uploaded image, so there’s not really multiple fields like it appears.
Sure enough; I just discovered this for myself when running some tests. I also noticed that Lemmy offers an Alt Text field, which it looks like the bot is already populating.
Test 1 : The URL field and the image attachment field were used; the latter overwrites whatever is placed in the former. I guess this might be modeled after Reddit.
Test 2: A direct link to the image at xkcd.com was placed in the URL field, and the source link placed at the top of the body. Result: This is similar to the bot’s current format, including the flaw that a desktop browser with strict privacy settings won’t show the comic image as part of the post when the thumbnail is clicked, because it’s an off-site image. Having the source link at the top of the body does at least make it a little more convenient to click through to xkcd.com’s single-page view.
Test 3: Only the image attachment field was used; the URL field was left blank. Result: This allows a desktop browser to show the comic image in-line when the thumbnail is clicked even with strict browser privacy settings, if the post is being viewed on the Lemmy instance where the post was made, because then it’s not an off-site image. Unfortunately, it’s still an off-site image when viewed on other Lemmy instances. The source link was again placed at the top of the body.
(Side note: I used m.xkcd.com links instead of plain xkcd.com links in these tests, just to see how the mobile site looks in different browsers. In practice, either ought to work.)
Conclusion: I don’t have one just yet. It would be helpful if we could direct all Lemmy instances to make their own local copy of a post’s attached image, to avoid the off-site image problem. Unfortunately, I don’t think there is a way to do this, and I suspect it would be too burdensome for some small instances.
Having the source link at the top of the post body is helpful, at least.
This will surely be used by the Trump administration to silence criticism of their unconstitutional, illegal actions.