https://github.com/Audiveris/audiveris seems to be a useful tool. It opens the scanned sheet music and does something to it. According to the manual, it can export to MusicXML. Then there are tools to convert that to LilyPond format.

There's a long discussion about written music formats on Commons.

More reading material:

• LilyPond on Commons help
• {{LilyPond_source}} on Commons
• Example file using it

ON WIKIDATA:

• Property LilyPond notation.
• Property musical quotation or excerpt. It also uses LilyPond format, so what's the difference? Used e.g. here.

I would suggest that Sebastian take the lead on this.

I think it's great if someone with knowledge on the subject matter can take care of this, yes.

The first thing to do is browse through the documentation – the links I posted, as well as anything else that looks relevant. What we learn from those will inform our decisions.

The main issues, as I see it now:

• The technical part of turning a scanned image / PDF to a structured format compatible with Wikimedia projects. How hard is it – can you achieve good enough results with one press of a button, or does it include a lot of manual work (by a musically-trained person). I assume the musical OCR will generate errors, as is expected with any OCR :) – but is it more "this doesn't make any sense at all, doing it by hand is actually faster" or "let's ask the community to help proofread those and catch errors"?
• Musical notation on Commons. I'm not even sure *what* our goal is here, so basically – what *can* we do? Examples of others having done it?
• Ditto about Wikidata.

We didn't upload anything, but the findings we did when researching this were included in the FindingGLAms white paper.

Chaining the project tag as I think this would still be valuable to do.