@junebug@kolektiva.social @imagecaptionspls also, for admins (or users with custom stylesheet add-on), you can add the following snippet to "Custom CSS", at the bottom of Settings > Administration > Site Settings. It'll show a red border around any images in the timeline without a description, so you and your users know what not to boost/check if it has a description in thread yet.

/* indicate images without a description */
.media-gallery__item-thumbnail img:not([alt]) {
border: 2px solid red;
}