People who are partially-sighted may not be able to see images of text very well. This may be due to there being little difference (or contrast) between the colour of the text and the colour of the background. Whilst the contrast and size can often be adjusted by the user when the text is part of a webpage, it is much harder, if not impossible, to adjust the text when it is part of an image. Therefore, it is important to check that an image of text has sufficient contrast before the webpage is published. The formulae necessary to calculate colour contrast are difficult to apply manually but there are many tools available that will automatically determine colour contrast.
If possible, avoid using images of text and use standard HTML text instead. Webpages are no longer restricted to a limited selection of fonts and there are many fonts available in a wide variety of styles. If an image of text must be included, then you can use a colour contrast tool to check whether the contrast is sufficient. Unfortunately, because many colour contrast tools work by reading the colours specificied in the HTML or CSS, they are unable to determine the colour contrast of an image. However, the tools often include an option to input colours manually. You can then use a separate colour picker tool to determine the colour of the text and the background in the image and manually enter these values into the colour contrast tool.
No example is available.