Digital photography We round up the month's most interesting questions about digital photography, ranging from use of a polariser and face recognition to Picasa 3, plus the best reader tips.

Where Are My Photos?

Picasa 3 seems to have lost a bunch of my photos. Is there any way I can recover them? Are they on my hard drive? Alyn McConnaha

First, let me come to Picasa's defense, Alyn. Picasa is unlikely to have lost your photos.

It's important to remember that photo organisers like Picasa, Windows Live Photo Gallery, the organiser in Adobe Photoshop Elements, and others don't actually store your photos. Instead, they point to wherever your photos are located on your computer.

When you start using an organiser for the first time, it will scan your hard drive, locate all your photos, and generate small thumbnails to represent each image. When you choose one of those images, your organiser finds the photo, still nestled away where you originally stored it.

The moral of the story is that you should never think "Picasa is storing my photos now, so the originals are duplicates" and try to delete them. If you do, you'll be deleting the only copies of your photos from your computer.

So what happened to your photos? The most likely explanation is that you deleted the photos accidentally, either in Picasa or in Windows Explorer. To be sure, you can search your computer for the photos. Hopefully you store your photos in the My Pictures folder (in Windows XP) or Pictures folder (in Windows Vista), which will make them easy to find. You can also search your PC for any JPEG files (Select Start, Search and try *.jpg).

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Understanding the polariser

I'm finding the effect of my polarising filter to be subtle to the point of invisible. It doesn't seem to reduce reflections at all. Can you explain? Jerry Heiss

Ordinary light, unpolarised, causes reflections in glass and water, and contributes to low contrast, hazy-looking skies in your photos. You can use a polariser to reduce or eliminate reflections and punch up the skies.

A polariser is a circular polarising filter that you screw onto the front of your camera lens. You can spin it around, and it has a variable effect depending upon its position. The effect on your photos is based on a number of other factors, including where the sun is and the angle you're making with respect to the reflections or the sky. To get the right effect, you need to consider all of these factors when you frame your photo.

Next page: face recognition and readers' top tips >>

See also:

Tutorial: Master digital SLR photography

Photo FAQs: improve your digital photography

Camera reviews