I'm not quite sure I follow what you mean, so I'll provide some general information here
Once you set up your products in E-junkie Seller Admin, we provide you with ready-made HTML codes for your cart buttons. You would simply copy the codes from us and paste them into the HTML source of your own Web site pages, wherever you want our buttons to appear among your own layout, text and images.
The top of this help page explains how to modify our standard button code to replace our standard button image with a custom button graphic or text link:
We do not have a way to specify an alternate button image that would automatically be included in the button codes we generate for you. However, if your site is built in WordPress, the WP E-junkie plugin makes it even easier to add our cart buttons to your pages, and that has a way to specify a custom button image that it would use for all the cart buttons it inserts in your pages: