1. Create a new image that is exactly 772 x 250 pixels.
2. Save the image as a PNG file with the name banner-772x250.png.
3. Right-click on a file explorer and select the TortoiseSVN | Repo-Browser menu.

 

4. Enter the address of your plugin repository. For example, for a plugin named Book Reviews, the address would be http://plugins.svn.wordpress.org/book-reviews.
5. Create a new top-level directory named assets, at the same level as trunk, tags, and branches.
6. Select the assets directory, then drag and drop the new image file in the folder to upload it to the server.
7. Specify a Log Message in the dialog that appears to explain why the file is being uploaded.
8. Create smaller images that are exactly 256 x 256 pixels and 128 x 128 pixels in size and name the files icon-256x256.png and icon-128x128.png, respectively. The larger icon should be a higher resolution version of the exact content of the smaller one, since it will be used to replace the smaller one on high DPI displays.
9. Repeat steps 6 and 7 to upload the two icons to the assets directory.
10. Visit your plugin's page on https://wordpress.org to see the images in place:

11. Search for your plugin through the https://wordpress.org/plugins page or the Add New section of the Plugins management interface of WordPress to see how the icon and short plugin description are used: