We've introduced ALT text to provide an alternative way of conveying the information provided by an image to Looop users that can't necessarily see the image.
To implement this, go into edit resource and click the image you wish to add ALT text for. A pop up box will appear underneath the image where you can add your text:
Once you're happy with your text, publish your resource. To double check your ALT text is appearing, go into the live version of the resource and hover over the image: