You have an audio file lasting a few minutes, and an image you want to show for the duration and render the project as a video format.
Import an image onto a blank track. To do that, you can use the usual insert media command, ensuring to view all file types.
Set a time selection of the length you want to display the image for.
Select the image item and hit Control+Alt+F to stretch item to fit selection. Render as the desired video format, and seeing as its a static image, you should be able to save a bunch of time and drive space by rendering at 1 FPS (frames per second) with no loss of image quality.