Icons8 Background Remover - Quickly remove the background from any photo
Optimage - Advanced image optimization tool
ClippingMagic.com - Remove image backgrounds online. Make backgrounds transparent, white, etc. Edit, crop, rotate, fix colors, add shadows, all you need for great photos!
ImageOptim API - Web service for image compression
Trace by Sticker Mule - Remove the background from any image for free
Imagify - Optimize and resize images online and through your CMS.