From site:  Paint.NET is free image and photo editing for computers that run Windows. It features an intuitive and innovative user interface with support for layers, unlimited undo, special effects, and a wide variety of useful and powerful tools. An active and growing online community provides friendly help, tutorials, and plugins.

It started development as an undergraduate college senior design project mentored by Microsoft, and is currently being maintained by some of the alumni that originally worked on it. Originally intended as a free replacement for the Microsoft Paint that comes with Windows, it has grown into a powerful yet simple image and photo editor tool. It has been compared to other digital photo editing software packages such as Adobe^® Photoshop^®, Corel^® Paint Shop Pro^®, Microsoft Photo Editor, and The GIMP.

From site:  Welcome to the morguefile classroom. Do you want to learn the basics of photography or improve certain camera skills? Do you wish to contribute to a growing knowledge base for photo enthusiast. With the morguefile photography classroom you can begin to take better photos of any subject and get more enjoyment from your photography.

From site:  GIMP is an acronym for GNU Image Manipulation Program. It is a freely distributed program for such tasks as photo retouching, image composition and image authoring.

GIMP is expandable and extensible. It is designed to be augmented with plug-ins and extensions to do just about anything. The advanced scripting interface allows everything from the simplest task to the most complex image manipulation procedures to be easily scripted.

From site:  PHOTO OP is a two-part interactive activity that introduces you to digital photography and digital photo editing. Use the virtual camera to create snapshots and explore lighting, focus, shutter speed, and compositional effects. After you have taken some photos, transform your pictures into something completely different.

This Art Zone interactive is suitable for all ages. You can take simple snapshots or create complex artistic compositions by layering, applying filters, and experimenting with various special effects, lighting, and blends. If your Internet connection is slow, allow the program to load fully, then come back to play.

This lesson for middle school students is designed to help them understand the principles and elements of composition – Balance. Emphasis. Movement. Unity. and Repetition – and use them in their own images.

From a historic perspective, photographs help students understand milestones of history, such as the Holocaust, the Great Depression, and the Civil Rights Movement. Powerful images can inform English class discussions of literary themes of rebellion vs. conformity, innocence vs. experience, racism, and national identity. In science classrooms, students could study photographs depicting the impact of humans on the environment. And in math class, students could learn about proportion, symmetry, and basic geometry concepts.