It might be a good idea to allow .webp as an extension for images to upload here. They are typically smaller in size than PNG or JPEG. It is an open format, and widely supported in common web browsers.
developers.google.com
en.wikipedia.org
An image format for the Web | WebP | Google for Developers
Learn about this image format that creates smaller images for the web and get links for converter downloads and support.
developers.google.com
WebP - Wikipedia
en.wikipedia.org