Meetable has a nice simple upload UI to add photos to events which works great on mobile. It even has an input field to enter image alt text right below the photo! However the one line input field is often too narrow on mobile displays (e.g. iOS/iPod) for good descriptive alt text.
Instead of a one line input, Meetable should use a multiline (try 3 lines) textarea for easier entry of more descriptive alt text.