So Jennifer Wren was trying overlap images in
https://textadventures.co.uk/forum/quest/topic/l37yrkzjteubaueganipba/overlapping-images

Although daeun solved it in the above link but it was unfortunately a workaround code,
the real code should be

s = "<div style=\"position:relative;\">"
s = s + "<img src=\"" + GetFileURL("pic-173083033507399949.png") + "\" style=\"position:absolute;top:0px;left:-200px;\" />"
s = s + "<img src=\"" + GetFileURL("pic-174128234075392960.png") + "\" style=\"position:absolute;top:0px;left:+200px;\" />"
s = s + "</div>"
msg (s)
msg ("You are in a room. A large room, entirely white, nothing here but a gravestone.")
msg ("Your gravestone.")

A very short demonstration is available at
https://textadventures.co.uk/games/view/57zl3sqjdeoeuqwqok9r5q/test

Credits to both XanMag and The Pixie
First I played XanMag's game
https://textadventures.co.uk/games/view/azkg8ntdweivkndr5j-ycg/quest-text-adventure-tutorials-and-templates
This game teaches game creators on various topics about game creation,

one of the teaching topic linked to The Pixie's forum post guide on How to control how images are displayed
http://textadventures.co.uk/forum/samples/topic/5566/how-to-control-how-images-are-displayed

Besides teaching on how to overlap images, The Pixie also teaches on how to make picture transparencies, wrap text around an image and possibly others that I am too lazy to read =D