I'm considering delivering online art tutorials and was thinking of using Lernid when I noticed that it's specifically for Ubuntu-run/related events. Is there any desktop software similar to it?
Lernid is by no means "specifically for Ubuntu-run/related events" - it is a "desktop application to participate in online learning events". Lernid's code shouldn't need modifying to allow you to setup your own events.
There is some information on how use Lernid for "your own purposes" on the Ubuntu Wiki.
As far as I'm aware Lernid does not have specific support for images and video, but it can show "Powerpoint slides" and also webpages. So between these you should be able to show images and video.
I think Lernid is almost ready to do what you need and it's easy as pie python code.
So what I think you need to do is talk to some of the programmers involved in Lernid and perhaps some other developers who might be good friends of yours. See if you can get the small amount of modifications in place to support your use cases and at the same time help lernid become more useful outside of the ubuntu classroom use case.
For development see the project page: https://launchpad.net/lernid