For those of us who are not designers and professional bloggers, the secrets of markdown, presentation templates, sizing pictures and finding pictures under creative common license has been quite a smashing experience. For most of us, a mobile platform such as an iPad is the go to device for posting. This makes things even more limited. I have not yet found a site for free medical images for my posts. I did find other great sites that give free access to great pics. I will list them here. I am only listing sites from where you directly click on image and save it to your images for reuse without joining the site. As such I will not make mention of sites like unsplash.
Pixabay. Perhaps the most well known. Great images.
https://pixabay.com/Pexels. Very well categorized images.
https://www.pexels.com/Stocksnap. Impressive collection.
https://stocksnap.io/Burst. It is by Shopify and has business/ project oriented images.
https://burst.shopify.com/Freestocks. Large searchable collection. High quality images.
https://freestocks.org/Skitterphoto. Another fantastic site.
https://skitterphoto.com/Life of pix.
https://www.lifeofpix.com/
I loved this pic from the site.
Picjumbo. I found the site a bit difficult and searches often did not produce results to my liking. Nevertheless it is a great free site.
https://picjumbo.com/IM FREE. A curated collection free for commercial use. Attribution often required. Splendid photos.
http://imcreator.com/freeShotstash. Unique photos, nice collection. Easy to navigate.
https://shotstash.com/
Kindly carefully read the rules on each site as attribution may or may not be needed.
Hope this helps improve your post quality.