Social Media Logo
You can upload a Social Media Logo for your convention, at Convention Tools => Convention Setup => Contact Info. This is a different logo from the header image which you can upload for your convention's theme, which is used only onsite at Tabletop.Events.
Purpose of Logo
The Social Media Logo will put your convention's logo into the page when your convention gets linked onto social media pages like Facebook and Twitter. If you do not upload a social media logo, the Tabletop.Events logo is used. (That's the image below, without the red line.)
How To Design
Your convention's social media logo must be exactly 500x500 pixels square, but other than background color it should not use 0 through 125 pixels vertically, and 375 through 500 vertically. See this image below? Your logo should only appear inside the red line. (But you should not have the red line in the image.)
The reason your logo needs to be square is that in a lot of cases the social media sites will display your logo as square. However, the reason you cannot use part of the image is that it will get cut off in some situations. Because sometimes, especially on Facebook, the logo will be represented as a rectangle, which will hide the top 1/4 and the bottom 1/4 of the image.