The art post tem­plate looks for any image attach­ments on that art post and places the found images into the slideshow.  So in order to place images into the ‘about’ con­tent of an art post you must first attach the image to a dif­fer­ent post (like this page) so that the image becomes an attach­ment of some­thing oth­er than the art post and there­fore will not wind up in the art post’s slideshow.