Hey there Jacques here from Support Engineering.

Currently, Intercom does not support the functionality to make images in articles display as pop-ups or in full screen when clicked. The images will open in a new tab if they are linked to a URL. To avoid having the image redirecting to a specific link and taking the user away from the article, there is no alternative provided at this time. However, the desire for having control over how images behave, such as displaying them in full screen, has been recognized as a valuable feature request and our Product Team is aware of it!

Regarding resizing images, you can upload an image and then click on it to resize it within the article editor. This may help to make the image appear larger within the article itself, but it will not enable the image to display in full screen upon being clicked.