All images we view on the computer will fall into one of two categories, either Bitmap or Vector. They both have their advantages and disadvantages so it’s understandable that they are used in different situations.
When most people think of making graphics they think instantly of the issue of quality, however you should take into consideration the matter of size. When creating a website you need to make sure that the size of the image will allow it to be downloaded quickly, and in the days of broadband internet this shouldn't really be an issue but is still go practice to think about it.
The most common type of bitmap image is a photograph. Every image picture that is taken with your camera will produce a bitmap image. All a bitmap image is a collection of pixels with difference colours assigned to each one, which makes up and image when put together. This is the main reason that the quality can be poor when the image is enlarged. In the day and age of high mega-pixel cameras and HD this shouldn't really be a problem providing the image is view with the correct dimensions. Bitmap images can only display 256 colours and this sometimes has an effect on the colours displayed.
The most common software that is used to create and edit bitmap images is Microsoft Paint. However if you use Adobe Fireworks you will find that the tools are divided up into vector and bitmap.
The most common file types that a bitmap is saved in is usually a jpg or jpeg image. There are others used including gif, gif (animated) and tiff.
Overall bitmap images are used to either create small animation or photographs. They are also used in a lot of websites.
Vector images are not as commonly used as bitmap however they tend to be of higher quality this is mainly because of the way they are made. They are created using co-ordinates and mathematical equations. Unlike bitmap images a vector image can be any shape, a bitmap is usually restricted to being a rectangle.
When a vector image is either enlarged or reduced in size it will retain its quality. To do this the computer will just change the numbers involved in the mathematical formula.
Vector images especially complex ones tend to be of a lot higher file size than a bitmap, and as a result if they were online would require a lot of bandwidth.
The most commonly used software for creating a vector image are AutoCad and CoralDraw although there are others available.
To summarise it depends on the situation on whether you should use one of the other but in most cases there is a combination of the two used. Providing the download speed is good and the quality of the image is too there shouldn't really be a problem.