How do I open image file stored on gitHub?

You don't need to use AJAX. You can put a URL directly in the Sprite's 'Load image' action.

The URL you shared is actually to a HTML page that contains an image, so cannot be loaded as an image itself. The direct link to the image is this: https://raw.githubusercontent.com/cybersurfer5000/image_test/a94534768231f675818f0ab67244a9ac7ade3e56/image1.png

(right-click the image and open it in a new tab, and that URL appears in the address bar)

Thank you!