Hi, Joanna.
A user should be able to input raw HTML for an but to make this easier in the Visual editor tab–and to allow uploading to the site’s WP Media Library, you could request this as a new feature (or maybe search to see if the idea was already posted by someone else) at our plugins’ UserVoice page.
This allows others who are interested in that feature to easily voice their support. We frequently review suggestions there to find out which ones are popular, then we implement as many of them as we can.
If you post it / find it, feel free to link to it from here in case anyone comes across this forum thread in the future.