Notes from OP:
"I've noticed a bug in the H5P.Image library that can be a problem when using text-to-speech tools like ReadSpeaker:
If the content author enters an information for the alt attribute of the image ("alternative text" in the editor), but not for the title ("hover text" in the editor), the resulting <img> tag has an empty title attribute like this: <img src="..." alt="my alternative text" title/> This leads to problems with the accessibility tool that we use on our website (ReadSpeaker), as it doesn't read the alt text in these cases, but nothing at all. I think the title attribute should not added to the tag in the first place, as an empty title attribute makes no sense."
Issue is reported here: https://h5p.org/node/1046851