Hi JohnnyMidrange,
I just did some testing and I got it to work with a PayPal Buy Now image.
1. Use this for the submit button:
[submit " "]
2. You need to add some custom CSS. Most themes have a place in their settings menu where you can add CSS. If not you can usually add it to your theme style.css file. However each theme is different.
But here is the code you would need to add:
.wpcf7-submit {
width: 107px;
height: 26px;
border: none;
margin: 0;
padding: 0;
background: url(https://www.paypalobjects.com/en_US/i/btn/btn_buynow_LG.gif);
}
input[type="submit"] {
background-color: #fff;
}