Here’s how you can display retina-ready images on your WordPress.com site.
First of all, what are Retina-ready images?
Retina-ready images are basically just high-resolution images for Retina HD display devices such as the iPhone 6.
This technique should work with any WordPress theme and should work for blogs hosted at WordPress.com as well as self-hosted blogs.
1. Create an image and make the width and the height twice the size of what you want to display it at.
(So if you want your image to display at 200 x 300 pixels, create an image 400 x 600 pixels.)
2. Insert the image into your post or page.
3. Go to image properties.
4. Change the displayed image size to half the width and half the height.
(In our example, the displayed image size would be 200 x 300.)
You can also modify your CSS to show high-dpi images.
Please read these threads to see how it’s done via CSS: