Images on blog posts
I couldn’t find any conversion research on this, but I am sure of it: using quality images in your blog posts makes you sell more of your stuff. Why?
Images improve readability and general user experience (breaks patterns, catches attention, eye candy, worth 1000 words etc). Posts without images are boring, and lead to less reading.
The more people read your stuff, the more they like you, the more they develop a relationship with you, the more they trust you and that all moves them further along in your sales funnel (doesn’t even matter what the funnel is like).
My advice: always use images in your blog posts.