how to add scrolling image on my website

They have: 2 posts

Joined: Apr 2013

Hello friends
i have a website,

i want an image to be on side of the
i want it to scroll down
when website visitors
scroll down the page,
(is that an overlay?)

i.e., i want it on side,
of the webpage but stay at top left
even if visitor
scroll down

How do i do it?
what is it called technically

Great thanks in advance