jekyll-image-size

https://github.com/generalui/jekyll-image-size

Jekyll tag-plugin to read image sizes from static assets and output in many formats. Generate your opengraph link-tags, img-tags, css, html props, or just output the width and height of an image. All output image-sizes can be scaled for retina support (/2 for @2x retina, /3 for @3x, etc...).