Almost all computers are installed with a set of fonts which have been put there by the computer manufacturer as the default for the operating system that computer is using. It should be noted however, that different computers may have different sets of fonts installed. If a visitor to your website does not have your nominated font installed then their browser will attempt to select a similar (possibly unattractive!) alternative.
The two most widely used operating systems today are Windows and Mac OS X and each of these come installed with different fonts! The solution to this problem is to use web safe fonts and all web designers should use these web safe fonts to eliminate the risk of an ugly default being used instead.
Web safe fonts are highly common fonts which can be found on almost all computers available and as a general rule should always be used all the time. However, there will be occasions where a font must be used that isn’t considered to be “web safe”. For example, this may be if a certain font is used in a companies logo or signage. To enable the viewer to see the font properly the best option for the web designer is to use an image. An image can be created from any font and the viewer will see it the way it should be. The downside of this though is that the text cannot be selected or highlighted, and screen readers used by some disabled people cannot read this text.