By default, a new GitHub App will have an automatically generated identicon. An identicon badge looks something like this:
After you create a GitHub App, you can customize your app's badge by uploading a logo and selecting a background color. A badge is a square logo image inside of a circular badge. You can choose a background color for the badge, which can visually distinguish your app.
Your logo should be a PNG, JPG, or GIF file under 1 MB in size. For the best quality rendering, we recommend an image size of at least 200px x 200px. See "Tips for logo and badge images" for more guidance on customizing badges.
You can change a custom badge for a GitHub App that already has an approved Marketplace listing by navigating to https://github.com/marketplace/manage.
To create a custom badge:
In the upper-right corner of any page, click your profile photo, then click Settings.
In the left sidebar, click Developer settings.
In the left sidebar, click GitHub Apps.
To the right of the GitHub App you want to modify, click Edit.
In "Display information", drag-and-drop an image from a local folder or click Upload a logo to select an image from your computer.
Crop your picture. When you're done, click Set new avatar.
In "Badge background color", type the hexadecimal color code of the background color for your badge. Note: The "Badge background color" input field will only appear after you upload an application logo.
For more information about creating a Marketplace listing for this app, see "Listing on GitHub Marketplace".