Adding a custom background image to your 2 by 2 Grid questions in Mentimeter is easy (this feature is available for all Pro, Conference, and Teams accounts).
In the Edit view, add a new slide and select the 2 by 2 Grid Question type. Then, in the Content menu on the right, scroll down to see the option 'Custom grids'. Here you are given the option to upload an image of your choice that will be used as the background for your 2 by 2 Grid.
Once you have uploaded the image of your choice, you can use it as a custom background for your 2 by 2 Grid Questions.
Please note: Any image you have uploaded will be available for other members of your organization to see and use.
It is also recommended that you upload only square-shaped images when creating your custom background. This will make sure that your image displays correctly and prevents any unexpected cropping of the image. For more information about recommended image formats and sizes in Mentimeter, please visit here: What format should the image I want to upload be in?