Too much text is difficult to read due to its size for most people and becomes almost impossible, if not completely impossible, to read for individuals with limited or no sight.
Instead, use the post itself to put out your message and leave the image to stand on its own or have minimal text. Think of the image as a billboard. Most effective billboards have very little text so people driving by can easily get the main point without having to slow down.
When adding your image, social media platforms will give you the option of adding what’s called alt text. This is behind-the-scenes text that an assistive reading device will read aloud to anyone, including those with limited or no sight, who may not be able to fully see the image to understand what the image includes. The reading device will also read aloud any information that you put in the post. If you put your message on the image itself (and not the post) and don’t include any alt text to describe the image, someone with limited or no sight would not be able to access the information.