Thumbr.io is described as 'powerful image thumbnails and processing on the fly for developers. Serve responsive images, cropping, compress, and generate website and doc previews' and is an app in the Photos & Graphics category. There are three alternatives to Thumbr.io for Online / Web-based and Wordpress. The best alternative is Imagify, which is free. Other great apps like Thumbr.io are ShortPixel (Freemium) and OptiMole (Freemium, Open Source).