Here is a collection of photos to use for decoration to music games content. For photos that are already in use in games and glossary, see the flickr section.
Flickr
You can easily find photos with proper usage rights on Flickr, especially in a section of Commons where all the photos are (mostly because of age) in public domain. Their style is often fitting for decorative purpose.
Unsplash.com
It is a useful resource with liberally licensed photos. Here is a collection of works that relate to our topic.
https://unsplash.com/collections/10515583/music-games-%2F-game-pieces
Be aware if you look for unique decoration, many of these have already been used for music games events.
Mastodon infographics/memes/banner-likes
The Practice Shoppe
http://thepracticeshoppe.com allowed us to use photos of their products as a decoration for music games content. The page itself is not only a shop but also a library of games for practicing music (for kids). If you need that kind of music games, check it out. On a page there is a lot of cool photos of different music dice.
Your own work
If you have something that may be useful for music games, upload it here (attach it to this page with "Files" button below). It will be accessible from other pages with image command.
If you think anything should be added to this subpage, please drop a hint or a link for future editors.