Images and multimedia

Consider the pros and cons before using images and multimedia

convey information more quickly than when using text
make complex information simple
enhance online teaching and learning
enhance communication with some disabled groups, particularly those with learning difficulties or cognitive impairments.

Multimedia is necessary if you want to show movement or change over time or demonstrate three-dimensionality.

Avoid gratuitous use. Only use graphics when they provide a clear benefit for your users.
Use an appropriate graphic format. JPG and GIF use different forms of compression. Use JPG format for photographs and GIF for images that have large areas of solid colour. This produces the best quality image at the smallest size.
Use an appropriate size - height and width dimensions. You should be able to view the page on a screen resolution set to 800 x 600 without a horizontal scrollbar appearing. If a scrollbar does appear at this screen resolution, you may be using an image that is too large. Also, try printing out the web page, does it print with all page elements (including images) visible within the width of an A4 page?
Optimise - height and width. Crop and scale images to an appropriate size. Do not manipulate the height and width attributes of the image tag used in HTML markup to make images look smaller than they really are. Users still have to download the large image, and this approach can reduces the crispness and apparent quality of the image.
Optimise - file weight. Reducing colour depth will reduce the weight (size in kilobytes) of graphics. Balance colour depth and associated quality of the image against the need for a fast download time.

Use an appropriate format. Use formats that support animation only where you need to show movement, three-dimensionality or transitions over time. Using an animated format for a company logo is usually not necessary.
Use PDF only where it is critical to preserve the printed format of a document. PDF takes longer to download and it may not accessible to blind people using screen readers.
Use common formats and stay a version or two behind. Users are generally slow to upgrade, so save multimedia files so that they will be readable by an earlier version of the plug-in.
Don't force it on users. Some sites use scripts to detect whether users have certain plug-ins installed and send them to the multimedia version of the site. Users should be allowed to remain in control of what they want to see and what they're prepared to spend time downloading.
Provide an accessible alternative. Multimedia may not be accessible to some disabled users. In Australia there is a legal obligation to provide accessible alternatives to multimedia.
Provide previews of audio or video. Let users try before they buy or download.
Segment larger works into topical sections. Users may only be interested in a portion of your content, and this would allow them to download smaller and more relevant files.