The idea that Web visitors are easily overwhelmed also affects the use of images in your content. The saying that, "picture is worth a thousand words" is incredibly true with the Web.
As visually oriented as we are these days, often, more can be accomplished with a well placed, Web-optimized image than the verbal explanation. The important thing to remember is that any images embedded into the content should contribute to the content, not distract from it.
A note about Web-optimized images: It's fairly common for people to take images right from their digital cameras, scanners, or other devices and just slap them onto their Web site. The problem is that these images are usually optimized for print media by default, so their resolution and size are much greater than what is needed for the Web.
Let's side track for a moment and discuss resolution. Resolution is the number of pixels per inch (PPI) inside a photo. This actually refers to the "density" of the photo or in other words how heavy it is. Don't let this confuse you with the actual image dimensions. An image that is 300 px x 300 px at 72 PPI is about 4 times smaller in "density" than an image at this 300px x 300 px at 300 PPI.
These images have serious, adverse effects on a site's load time, unless they're optimized for the Web. Web optimization requires the photo to be ran through the appropriate software, downsized and re-saved in a new more compact format.
Once this has occurred the image can be placed on a web page and will load properly at nearly every given speed. Any web image that is going to be used should be no more than 72DPI and should be the actual pixel dimensions you desire them to appear on the site.
Avoid the temptation of using your Content Management System to dynamically resize the images. When your images have too high resolution and are not properly optimized for the Web, the result will be a site that loads VERY slowly and images that appear to load line by line, pixel by pixel. Don't let this happen to you!