A binary tiddler is a way to store non-textual content (such as an image, an office document, an mp3) in TiddlyWeb so that it is accessible as a tiddler. When the tiddler is retrieved, if no specific content-type is requested then the content will be delivered with the content-type with which it was stored. Thus, if an image is stored to a tiddler as image/png it will be displayed in the browser as an image when requested. If the text/plain or application/vnd.tiddlyweb+json media-types are requested, then the text field of the resulting output will be a base64 encoded version of the data.

See How can I use curl to create stuff in TiddlyWeb? for an explanation of how to PUT a binary tiddler to a TiddlyWeb server.