Searching for pictures at:
  Google images
getty images
How to search for good pictures:
  1. With google image, you can select "showing extra large images" option, pick the high resolution ones.
2. Content you want can be easily seperated out (mask out) from the background.
Workshops:
  Workshop 01
  Workshop 02
  PhotoMerge Material
 
Additional tutorial:
  intro_photoshop_workspace.pdf
  howto_generate_file_formats.pdf
  howto_resize_crop.pdf
  combining_images.pdf
  Using layers VIDEO tutorial
  Using layers
  Making and refining selections
  Using blending modes for photographers
  Making lighting corrections
  Creating PDF files