He Edward,
Yes, you can. Please see the images below, which will show you how I did it.
One thing to keep in mind while testing this locally: the logo in the below images is in the Mendix cloud (https://da42.mxapps.io/img/Layouts$DA42_images$DansAtelier42_logo___smaller_108_x_50.png). It will only be available to you locally after you deployed a version to the server with the images, in my case DA42_images.
Did you try filling in the image URL in the browser and do you see it then? If not, the image URL is not correct.