Add Image when User Hovers Mouse over a button

How do you mean Pop up?

Do you want the image to appear at the mouse or is the image to replace the button being hovered over?

i mean when the user hovers mouse over the button a little preview or pop up of a picture shows

I would use a tooltip script, such as Tooltipster.

There are demos on the site along with easy-to-follow instructions on how to implement it.

Hope this helps.

Thanks