Displaying images

I am reading Chapter 8 “Drawing Pixels, Bitmaps, Fonts and Images” of the red book OpenGL Programming Guide (5th edition).

I’d like to do the following:
[ul]1. Read a typical internet image (gif, jpg, png, etc) [/ul]
[ul]2. Display it on WebGL[/ul]
[ul]3. Do some manipulations on the image[/ul]
[ul]4. Read back the new (manipulated) image[/ul]
[ul]5. Save the new image into gif, jpg or png[/ul]

Where can I find a sample code and/or document to do (some of the) above?

Thanks in advance for your help.