Websites, blogs, and social media apps desire specific images sizes/file size requirements for cover art, logos, profile pictures etc.
Image resizing tools assist in adjusting pixel resolutions and cropping of your images or photography.
Image Optimizer - With this free online service, you can resize, compress and optimize your image files for optimized web pages, email attachments, or storage.
JPEGmini - 'Photos on a diet.'
Snagit by TechSmith - screen capture and rescreen recording tool