The Digital Photography School blog has an instructive tutorial on using layers for those just getting their feet wet inside Photoshop, or other high-end image editors like the open-source GIMP. Those jumping in will learn how to make transparent layers, use masked layers to roll back effects, and duplicate layers for sharpening and other effects. Hit the link for a quick schooling, including links to related lessons, or offer up your own tutorials and advice in the comments. Understanding Layers in Photoshop

Wikihow runs down how to make a digital image look like a sketch in Photoshop. Looks like a good photo transformation before you upload it to the Rasterbator.

If you've ever suffered from seeing a great photo sullied by red eye, reflective skin, or other blemishes, Wired's How-To Wiki is offering an assist. The guide provides specific steps one should take with image editing tools to fix distracting imperfections or backgrounds, and while the instructions are written from a Photoshop user's perspective, users of the free, open-source GIMP editor can follow along by finding the (usually identical) tools called for. Hit the link for a lesson, or contribute your own revisionist tips at the wiki. Photo by Noel Zia Lee. Touch Up Your Pics

Frequent Photoshop users can save time and energy using automated Photoshop actions when processing images. The Epic Edits weblog explains how. First, make the actions palette is visible, and create a new action. Then, record all the steps you want to automate on one image, and stop recording when you're finished. Once your action is complete, then you can use it on any images going forward, without repeating the steps again. How to Create Photoshop Actions

Professional Photographer Magazine has a relatively easy to understand long but helpful guide to histograms, the graphs that show what levels of light were captured by a digital camera's sensor. Along with detailing the changes that happen when you export to JPEG files, the guide introduces a concept that, while debatable, has found favour with some professionals—"expose to the right," or shooting a photo strategically over-exposed to capture detail and then adjusting it later in editing software. If you've ever wondered how the strange graphs in Photoshop or your camera's screen relate to good and bad photos, this guide can help demystify the process.
How To Read and Understand a Histogram