What I do when I'm creating my own images I number them and once they're up I delete them from my computer but I keep the last image as a bookmark so if I do more for a certain page I'll remember where to start from.
When creating the images from scratch, I use a key called "PrtSCan/SysRq" which snapshots everything displayed on the monitor. this key is located on the top right side of the keyboard depending on what type of computer you use. Using programs like Photoshop or Illustrator you can edit the images to the way you want them and sometimes change their diamiter ready to display on the web.
Its very easy once you figure out what to do but I try not to get carried away, don't want to make too much.