Bulk Image Resizing Made Easy 2.0 (Online & Free).
BIRME is a flexible and easy to use bulk image resizer. It can resize your images to any specific dimension and crop them proportionately if necessary. It's an online tool and you don't need to download or install on your computer. BIRME is absolutely free to use.

One image for all screen resolutions and different devices is not enough. An image per pixel is too much - so how can someone automatically choose the optimal responsive image sizes?
Responsive websites, even the most modern ones, often struggle with selecting image resolutions that best match the various user devices. They compromise on either the image dimensions or the number of images. It's time to solve these issues and start calculating image breakpoints more mathematically, rather than haphazardly.

Optimize images for web on the fly.
imgproxy is the blazing fast and secure image processing tool.

croppic is an image cropping jquery plugin that allow users to resize and crop they uploaded pictures.