For the best image performance it needs to be prepared for a specific destination. There are several main images and picture sizes that are recommended to use by Twitter. And here is an April 2019 update. The main profile picture or avatar needs to have aspect ratio 1:1 and recommended dimensions are 400×400 pixels. Twitter cover suggested dimensions remain 1500×500 pixels. Twitter image post size to support mobile platforms is no longer supports 2:1 ratio. Today's recommendation is aspect ratio: 16:9 with minimum 600 X 335 pixels, abut better 1200 X 675. Twitter image card size or shared link image size correct ratio is 1.91:1 with best fit 1200x628 pix. Single Image Tweets and GIFs for posts and adds for best show including mobile devices recommended aspect ratio is 16:9 with minimum size of 600 X 335 pixels and better 1200 X 675 pixels to support high resolution displays. Check Twitter developer pages for updates.