There's a "Custom message on register form - HTML allowed" option in the 'Users' section of the admin panel. You can insert any HTML here including an <IMG ...> tag.
Welcome to the Q&A site for Question2Answer.
If you have a question about Q2A, please ask here, in English.
To report a bug, please create a new issue on Github or ask a question here with the bug tag.
If you just want to try Q2A, please use the demo site.