NPM package here

npm i gitbook-plugin-insert-logo

The following plugin inserts a logo into the navigation bar (above the summary and above the search input). Simply, drop a logo.png file into the root folder of your GitBook and add this plugin into your book.json:

{
    "plugins": ["insert-logo", "another plugin 1", "another plugin 2"]
}

You will also need to provide url for the logo. The url can be local file, a remote URL, or base64 hash. Add the url into the plugin configuration in your book.json:

{
    "plugins": ["insert-logo", "another plugin 1", "another plugin 2"],
    "pluginsConfig": {
        "insert-logo": {
            "url": "http://www.example.com/my-logo.png",
            "style": "background: none;"
        }
    }
}

You are most likely using relative paths for your logo in the config. The path is relative to the current page. This can also happen with nested TOC. Consider using absolute path (the url to the file starts as: /logo.png instead of logo.png), or use base64 (see example below).

(The example gif encoded as base64 is taken from example here: https://css-tricks.com/data-uris/)

"pluginsConfig": {
    "insert-logo": {
        "url": "data:image/gif;base64,R0lGODlhEAAQAMQAAORHHOVSKudfOulrSOp3WOyDZu6QdvCchPGolfO0o/XBs/fNwfjZ0frl3/zy7////wAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAACH5BAkAABAALAAAAAAQABAAAAVVICSOZGlCQAosJ6mu7fiyZeKqNKToQGDsM8hBADgUXoGAiqhSvp5QAnQKGIgUhwFUYLCVDFCrKUE1lBavAViFIDlTImbKC5Gm2hB0SlBCBMQiB0UjIQA7"
    }
}