Price
You can spend anywhere from about $100 to $5,000 on a digital camera. Short of professional level or some specialized need, a good camera will cost you $300-$400.

Size
My Canon SD500 Digital ELPH weighs only 6 oz, while my Canon Digital Rebel with it’s interchangeable lenses weighs about 5 lbs. I’ve always recommended the 12” PowerBook over the 15” or 17” on the premise that the smaller and lighter it is, the more you’ll use it. I seldom travel with my single lens reflex (SLR), because I don’t want to lug it through airport security or haul it on my bicycle. I tend on the other hand to carry my ELPH with me everywhere I go. The SLR takes better pictures, but not if I don’t have it with me. The weight and bulk of a digital camera is of critical importance. On a film camera, you wanted to use at least 35 mm film in order to meet minimum standards of picture quality, so the camera had to be big enough to accommodate 35 mm film. If you went smaller, you had to use smaller film sizes, so your image quality suffered. The size of a digital camera doesn’t correlate anywhere near as much with quality. You can produce excellent photos from a compact digital camera. When you want to use the lenses from your film camera or other interchangeable lenses, however, you’re back to the bulk of the film camera. The digital single lens reflex (SLR) cameras are almost as bulky and heavy as their film counterparts. The greater the zoom lens magnification and the more bells and whistles (features) on a digital camera, the bulkier the camera is going to be.

Resolution
The resolution of a digital camera is stated in “megapixels.” Consumer digital cameras currently range from about 2 megapixels to 8 megapixels. The screen on an iBook or 17” monitor is typically 1024x768 pixels. That’s not quite one million pixels or one megapixel. If your digital photos are viewed only on your 1024x768 screen or used only on the Web, you need only one or two megapixels. If, however, the images are going to be printed out, you’ll need more (see Chart A below). Don’t buy a camera solely on the basis of pixels. Just like megahertz isn’t a good measure of a computer, pixels aren’t definitive in choosing a digital camera. Not all pixels are created equal. The images from lower quality digital cameras suffer from problems like “barrel distortion,”purple fringing,” and “artifacts,” so it behooves you to check the reviews on the camera you’re contemplating.

A 3 megapixel camera will do just about all you need for Web publishing or email, and will support small prints. 5 megapixels has become the norm. For professional use, 6 megapixels is the minimum.

Optical viewfinder
In my opinion, don’t buy a camera that doesn’t have an optical viewfinder (e.g. Nikon Coolpix S1, Sony Cyber-shot DSC-T series). Some of the compact digital cameras have only an LCD for previewing the image. Some LCDs fare poorly in bright sunlight and they all hog power. I keep my LCDs turned off to make my battery last longer.

Manufacturer
The major players are Canon, Nikon, Sony, Olympus, Konica/Minolta and Kodak. As you can see from my list below, there are others, but for the most part, I’d avoid the less popular brands unless a particular feature makes one of their cameras stand out for you.

Memory
There are two main forms of digital memory card: Compact Flash and Secure Digital (usually shown as “SD”). Generally speaking, Compact Flash is used in high-end SLRs, while SD is most common in point and shoot cameras. Sony uses a proprietary and therefore more expensive “memory stick.” Fuji and some Olympus cameras use xD cards, another proprietary format. The SD format is gaining in market share, even at the high end.
Whatever memory card a camera uses, you’re going to want a much bigger card than the 32 MB card that typically comes with the camera. Only eight 5 megapixel images will fit on a 32 MB memory card, while 140 will fit on a 512 MB card and 280 will fit on a 1 GB card. The cards are relatively cheap, so you should buy at least two of the largest ones you can afford. CompactFlash cards range up to 8 GB. SD cards range up to 4 GB. Some cameras handle images more quickly with the faster “Ultra,” or “Premium” cards. A fast 1 GB CompactFlash or SD card runs about $75-85 from Amazon.com.

Image storage format
Most digital images are compressed and stored in the JPEG format that is used on the Web. If you’re shooting for print publication, you may need to have RAW images that can be manipulated more. Most compact consumer level cameras do not support RAW images. For those, you typically need to go with the SLRs.

Software
iPhoto has rendered the manufacturer’s image software offerings unimportant to a Mac user. I load my images - JPEG or RAW - into my Mac with iPhoto, then export them for editing via Photoshop. I never use the Canon software.

Batteries
Some cameras support the use of AA or AAA batteries in a pinch, while most use proprietary lithium-ion rechargeable batteries. Cameras with Li-ions are more compact and the Li-ion batteries last much longer. If the camera has a Li-ion battery, you should buy a spare (about $40-50) and keep it charged.