Eye catching images will always be shared on Facebook. The most shareable images are those that contain text on them. You do not have to be a Photoshop expert to add good looking text to an image.
Just use one of the following free design websites: 1. Canva
2. Pic Monkey
3. Word Swag
There are plenty of websites where you can find copyright free images as well such as pixabay.com and pexels.com.
You need to make the image and the message related to where you will send the user. So if you have a post on your website about avoiding costly mistakes in Internet marketing you could create a humorous image of a person with empty pockets and use the words “don’t make these costly mistakes with your online business”.