Use Few Colors In Your GIF's
Minimize the number of colors in your GIF images. GIF's can be stored with a maximum of 256 colors. Minimizing the number of colors to 16, 8 or even 2 dramatically reduces the size of the GIF-file and therefore improves performance. Choose as few colors as possible without ruining the image. You might test both reducing colors with error correction or by selecting the nearest color.
Use High Compression In JPEG
Improve the performance of your site by reducing the size of your JPEG-images. JPEG can be saved with different compression-percentages. A high compression results in a smaller file size but also in a less perfect image. Test several compressions for each image you want to use. For different images the acceptable compressions will differ.
Reserve Space For Images
Generally text arrives more quickly than an image. By reserving space for an image the browser is able to render the text. A visitor can start reading right away. Reserving space is done by defining the attributes vsize and hsize in the tag
Provide Thumbnails For Large Images
In some cases you do need large pictures that take a while to load. I.e. if you're running a website on modern art. In such a case do provide small copies of the original images (thumbnails) that link to the original ones.
Reuse Images
Once images are loaded they are stored in cache. If you use the same image in several webpages the image will be loaded the second time in a breeze. It is necessary to have the image in the same location. Also be sure to use exactly the same filename. Even if a browser can handle differences in uppercase and lowercase, your browser cache can not.
Provide Size Information
If you use large images, videos etc., give an indication of the size before the actual transfer begins.
You Can Not Reference Images From Other Sites
If you use images from another site (i.e. an image archive) do copy them to your own site. Looking up other servers to get the images would introduce overhead and an extended load-time.
You Can Not Use Large Textual Images
Avoid creating images of large pieces of text. It gives you more possibilities but it costs valuable bandwidth. If you do need textual images be sure to reduce the number of colors.
You Can Not Use Word Processors
Don't use word processors to write HTML. They really mess it up. It's not uncommon for a site to double or triple in size because tags are added unnecessarily by a word processor.
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