I already added a featured post image to all my posts (>1000). Some posts (around 700) still have an image at the beginning of the post content. 

Now I need to remove all images which are right at the beginning of the post content. I need to leave the images untouched which are not at the beginning. 

Because of that I can't just remove "the first image tag occurrence in the post" because then I would remove images from the post content. 

Maybe this plugin here https://wordpress.stackexchange.com/questions/142491/permanently-remove-first-image-from-posts could be used as a base but what would be re regex or query to reflect this requirements?