Images are nearly always the largest item on a page and if you have icons for “contact us” and “home”, a company logo, ticks or crosses, background images etc; all of a sudden you can have an overweight website, rather than a toned athletic one!
Proper Use: if you have an e-commerce site and as a result have thousands of product images, thumbnails, full size high quality Jpegs showing different angles etc; this will put strain on the server hosting the site. So you can use a frame in place of an image, the frame simply points to the image.
The benefit of this is that the page will load as normal but images will be loaded form another server, the page will look as it should even before the images load and loading times will be reduced because the server hosting the site will be running faster.
Improper Use: Using one large frame which essentially is the website, this will mean that your website will likely never be indexed because it effectively doesn’t exist on that domain.
Define Image Parameters: Setting the image’s width and height on page will help to reduce load times. Setting this will mean that the browser knowing in advance the dimensions of the image will reserve a place on the page for it.
Zipping and Compression: There are tools such as Smushit that are lossless zipping tools, these do not reduce image quality but instead provide you with a zip file for each image which should replace the original on your hosting server. This will increase website load times significantly.