You can add an image with each post. We actually encourage you to do so – see How to Write the Perfect Tweet for example.
Here are the size guidelines:
– 1200×630 pixels for a post on Facebook and 1200×627 pixels for the shared links
– 440×220 pixels (2:1 ratio) for an image in a Twitter publication
– 600×600 pixels for a post on Instagram
– 646×220 pixels for a post on LinkedIn
– 497×373 pixels for a post on Google+
All image formats are supported. You can use different formats for image sharing. E.g. JPG, PNG. Animated GIFs are only supported for Twitter.
The size limit on Twitter is 3Mo and on Facebook is 25Mo.