Digital Photography is in a class other than 'normal' photography. While traditional photography uses photographic media that reacts when exposed to light (creating a picture), digital photography uses a photosensitive plate that translates the wavelength of the light that strikes it into 1's or 0's, hence the name digital. Both forms of photography, however, use optical lenses to focus light onto the respective medium.
Digital vs. Traditional
The sequence of 1's and 0's that make up the photograph is called a file. The file, and effectively the photograph, can be reproduced perfectly and also transferred over the internet or other forms of digital communication without loss of quality.
The disadvantages of digital photography are directly related to limits in technology. To have a high quality image, you have to have an extremely large amount of 1's and 0's. The limiting factor is the plate that translates the light into digits. In first generation digital technology, the plates were not very good at digitizing the light, and so digital photographs taken with these plates look fuzzy and "squarey." In the past few years, however, technology has advanced so that the plates are much more effective at digitizing light, and pictures can be taken at much higher qualities.
The resolution of an image taken by traditional means is limited by the film it is taken on and the lens that focuses the light. Some film is better than others, and some lenses are better than others. While mild enlarging and cropping of a traditional photograph can be done in the darkroom without much loss of resolution, the sharpness and clarity of the image decreases as the image is enlarged and less of the surface area of the film is being used to create the photographic print. This does not refer to the effects of "zooming in" with a tele-photo lens, which vary greatly depending on the lens and can be just as sharp as any other kind of photo. Because the whole surface of the film is still being used when one uses a tele-photo lens the quality of the image will be equal to an image captured on the same film with any other lens of equal quality.
The resolution of a digital image is limited to the quality of the plate and to the quality of the lens in the same way that a traditional photograph is limited by the film and the lens. A higher quality plate records more information (measured in pixels or Megapixels), in the same way that a lower ISO film is able to record a higher resolution image. In the same way that a traditional photograph loses sharpness and clarity when it is enlarged, digital images that are later cropped either to alter the composition or "zoom in" decrease in quality as the resolution decreases and noise becomes more apparent. Lower-quality digital images are notorious, however, for losing quality much more rapidly than a traditional photograph.
One advantage that digital photography has over traditional is that digital photographs can be stored on a computer or a small data storage device. Because digital photographs are digital information they can be imported into sophisticated image editing software where they can be manipulated in both very simple and very complex ways. Traditional photographs must be developed on expensive film whether you want the picture or not, while digital photographs only need to be printed on photo paper if you want the image on photo paper. Also, the beauty of digital means that you can instantly see what your photograph looks like on some cameras that have an LCD screen for viewing, while traditional photographs have to be developed (greater expense and time) before you can see the image.
Naturally, however, there are also advantages to traditional photography that digital photography cannot replicate. Currently, the startup price for a serious hobbyist or fine art photographer wishing to do digital is much higher than a photographer pursuing traditional methods. For one to seriously begin working digitally and obtain high quality results they must purchase a fairly modern computer, expensive software, a printer, and a camera (serious digital SLRs have just recently fallen below $1,000USD), not to mention still having to pay for paper and ink. Whereas both old and modern film based equipment can easily be purchased for very low prices used while offering results that are of equal quality.
However, it is important to remember that the greatest diversity of images can only be reached by utilizing both digital and traditional, along with other alternative processes. Certain mediums are better suited for certain situations and at times it can be good to let go of some control by allowing a traditional medium to cause spontaneous effects outside of your control, while at other times it may be more appropriate to have the tight control of digital. If you never let the medium take some control then you will not have the opportunity to learn from your mistakes.