Enable Image Resizing
To use Image Resizing you first need to enable it via the Speed app of your Cloudflare dashboard:
Log in to the Cloudflare dashboard.
Click the account for the domain you want to use with Image Resizing.
Select the domain where you will be using Image Resizing.
Click on the Speed app.
Click the Optimization tab.
Under File Size Optimization, enable Image Resizing
If you do not want to resize images from any origin, uncheck Resize images from any origin.