State and local governments will often post documents on their websites using Portable Document Format (PDF). But PDF documents, or those in other image based formats, are often not accessible to blind people who use screen readers and people with low vision who use text enlargement programs or different color and font settings to read computer displays.

Among other things, the Americans with Disabilities Act (ADA) ensures access to the built environment for people with disabilities.  The ADA Standards establish design requirements for the construction and alteration of facilities subject to the law.  These enforceable standards apply to places of public accommodation, commercial facilities, and state and local government facilities.
Web designers often design in such a way that does not allow the user to adjust font size or color. While they may be protecting their brand, they are also inhibiting some users. Many visually impaired need to use high contrast color settings or very large fonts to read a website. Don't design your website in a way that makes it impossible for them to do this. 
Many people with disabilities use “assistive technology” to enable them to use computers and access the Internet. Blind people who cannot see computer monitors may use screen readers – devices that speak the text that would normally appear on a monitor. People who have difficulty using a computer mouse can use voice recognition software to control their computers with verbal commands. People with other types of disabilities may use still other kinds of assistive technology. New and innovative assistive technologies are being introduced every day.