If you ask for help with a faulty circuit board, contributors will often ask you for photos.
This is important early in the thread, so we all know what we're dealing with. In almost all cases, photos will help. We may also see something in the photo that points to a specific fault.
Here are some guidelines for taking photos of circuit boards.
1. FOR YOUR SAFETY, if the board has any large electrolytic capacitors (marked "LDE" on the picture below), DISCHARGE THEM BEFORE YOU TOUCH THE BOARD. See http://www.google.com/search?q=safely discharge a capacitor
2. If the board is dusty or has gunk, watermarks or impurities on either side, clean it using a soft brush, aerosol duster, and/or vacuum cleaner, and a soft toothbrush with isopropyl alcohol (tape head cleaner) or CRC IPA Cleaner, or for dirty boards, cotton swabs and CRC Contact 2000 or CO Contact Cleaner or similar.
3. Generally, include pictures of the inside of the whole piece of equipment, from above and below, especially if it contains multiple boards.
4. If possible, take the photos OUTSIDE on an overcast day, so the board is lit softly from all angles. Don't have direct sunlight on it. DON'T USE A FLASH.
5. Get the board(s) square in the picture - that is, (a) not rotated, (b) viewed from directly above the centre, and (c) with all or most of the text on the board itself around the right way. Sometimes we can trace out the circuit by combining top side (components) and bottom side (trackwork) photos, and that's easier if the photos are square, and line up properly.
6. Start with the whole board. Take one main photo looking straight down, and one of the underside. If there are lots of tall items on the board, take a few more photos at slight angles. Then take extra photos of areas of interest.
7. The copper tracks should be clearly visible, and the printing on the board should be readable. If necessary, take close-ups in areas of interest.
8. If there are small components mounted on the underside, make sure their markings are readable; if necessary, take close-ups.
9. Markings on semiconductors are important, so if they're not readable from above, take extra photos, especially of any that are attached to heatsinks. (Most black plastic components with three or more wires or metal leads are semiconductors.)
10. If you're handy with an image editor, you can mark up the main photo with the markings from the semiconductors, instead of photographing them. If the board is complex, you may want to add a grid on the main photo, to help with locating parts.
11. If a photo is rotated so its text is not readable, rotate it before you upload it. If you notice that it's wrong after you've uploaded it, you can remove the incorrect version and re-upload it, using the Manage Attachments dialog.
12. If there are important separate parts that connect to the board, please describe them, and where they connect to the board, and include a photo.
13. Photos should be in JPG format. You can attach them to your post for others to view.
----- MORE DETAILED INFORMATION -----
The picture above is an example photo of a switching power supply. Markings refer to the following list.
LDE: Large Dangerous Electrolytic. Sometimes these can stay charged to a dangerous voltage, even with power off. Usually they are mounted vertically, not like this example. Carefully measure DC voltage across it. If it's more than 10V, discharge it: http://www.google.com/search?q=safely discharge a capacitor. Electrolytics marked with a voltage of 35V or less aren't normally dangerous.
REFERENCES: If possible, these should be readable in the photo. Sometimes they are important - the marked one ("F702") tells us that the mustard-coloured component is a fuse, not a capacitor, which is what it looks like. References also allow us to identify components clearly, without having to describe them by their location.
SEMI: Semiconductor (not on heatsink). Any black plastic component with three or more leads is probably a semiconductor. The two indicated with arrows are a TO-92 transistor (or it could be a three-pin integrated circuit) and a power component that's not heatsinked. As for SOH, please give circuit reference and markings.
SOH: Semiconductor on heatsink. 1. Please mark the circuit reference on the photo if it's not clearly readable. 2. Please give the circuit reference and all markings on the component - marked on the photo, or in your post - or include a separate close-up of it.
TRACKWORK: We may need to follow the copper tracks, so they need to show up clearly. This is especially important on the underside.
----- EXAMPLES OF BAD PHOTOGRAPHY -----
These photographs, kindly provided by (*steve*), show several mistakes and how they affect the image. Steve says "I think those were taken with my EOS 450D. The lens really is the cheapest available Canon lens [...]".
The photo below was taken using a flash. You can see the bright reflection. Much of the board is in the shadow of the tall items, because there is only one light source.
The photo below shows the underside of the board, taken with a flash. It's impossible to see the trackwork in the area of the reflection, and the rest of the board isn't properly illuminated.
The photo below shows insufficient illumination and camera shake.
The photo below is out of focus and is almost useless.
The photo below was simply taken from too far away.
The photo below was taken outside in direct sunlight. Many areas of the board are useless because they're shaded by tall items. This is why single light sources are no good.
The picture below was taken under an open sky, but without direct sunlight. Illumination is fairly even.
The photo below was taken outside, in the shade. Illumination is more even than the photo above, but make sure there's enough light for your camera to take a good clear picture. See how the board is square in the frame, and viewed from directly above.
The photo below is the same as the one above, but with its contrast and sharpness tweaked.
The image below is the same picture, at a higher resolution.
Thanks to (*steve*) and others for their help with this tutorial.