While researching a fairly boring IT product, I ran into a site with a product picture labeled “actual size”. Making that sort of claim online is always a bad idea. You see, the image has the same number of pixels whether you’re viewing it on a regular desktop monitor, or a small laptop or netbook screen, or even a mobile phone. But the size of those pixels will vary widely on each platform. Smaller screens tend to squash more pixels into a given amount of screen space, thus making each pixel smaller. As a result, the size of an image on the screen (measured in inches or centimeters) may be a lot different from one person’s computer to the next.

For similar reasons, it’s a good idea to avoid absolute claims about color, texture, and other physical attributes. Instead, show the item next to a common reference point that conveys its attributes no matter how good or bad the online picture looks. The people who sell small gadgets like cell phones know all about this approach. That’s why you’ll see size comparison tools — like showing the phone next to a deck of cards — on their sites. By giving people a familiar and tangible reference point, you provide the data they need to make a decision, without introducing any uncertainty about the product’s size and other key attributes.