What is JotForm?
JotForm is a free online form builder which helps you create online forms without writing a single line of code. No sign-up required.
At JotForm, we want to make sure that you’re getting the online form builder help that you need. Our friendly customer support team is available 24/7.
We believe that if one user has a question, there could be more users who may have the same question. This is why many of our support forum threads are public and available to be searched and viewed. If you’d like help immediately, feel free to search for a similar question, or submit your question or concern.
Currently, we do not have an option to set specific images when a form is shared via facebook. But let me escalate this request to the developement team. We'll let you know once we have updates on this.
For the meantime, if you have a web page where you can embed your form, you can add these meta tags to your header:
<meta property="og:image" content="[url to image]" />
<meta property="og:title" content="[page name]" />
<meta property="og:description" content="[content description]" />
Then this should pull up the information from you page and allow you to see your image as well.