That's actually how I initially planned for this to work because that "alt" icon looks like a button to me. One reason why I didn't go that route was because not all images with alt text show that icon, and I couldn't figure out why. It also doesn't show up on different types of media, like gifs (which show a "gif" icon instead).

I get that the warning message when there's no alt text is probably not helpful to a lot of people, but I like knowing if the tweets I interact with can be read by everyone. It helps me remember to ask people to include alt text next time, or to potentially include it myself. If there's just nothing there, I forget about it (which is exactly what happens when I use Twitter on my phone).

Thanks for the feedback!