When creating a test it is possible to upload and add an image to a test. This is only available in an essay question.
To do so click on the test you would like to edit click on add static element and then markdown. You will then see a text box with the option to add an image. Once an image has been added to your gallery you won't be able to delete it.
If you are looking to add an image to an essay question please create the essay question first and upload your images. Once done, this will mean you are able to add them to the test.