Stock images are the web design version of the 'green' business. You get to save money, reduce duplicated effort, get your results right away, and once you purchase a picture, it's yours to use again later if you like. The downsides are few and far between — but it can reasonably be said that the hardest part about dealing with stock photos is knowing when to use them and which ones to avoid.
DON'T fall for clichés
There is certain stock photography that are so perfect that they become imperfect. That striking picture of a dynamic handshake between two professionally dressed young adults? That's been on a hundred thousand websites. The classic Dodge Viper sitting out front of stucco three-story on a granite driveway lined with palm trees? Done to death, and on some of the cheesiest sales-letter sites on the 'net’.
DO communicate with your images
Have you ever heard a teacher or mentor say "show, don't tell"? The most effective stock photos take that to the next level — they don't just show, they reach out. A stock image of a real human being (not an over-glossed model dressed like one) that makes genuine eye contact with the camera and has an unforced smile will have a better effect for a website than seven higher-cost pictures of the prototypical model-as-yuppie that look generically dynamic and powerful.
DON'T use oversimplified images
It's all the rage right now to have stock images that show one thing on a white background, possibly with another thing for context. A woman sitting on nothing with a laptop on her lap, looking at it intently. A stack of silver and gold dollar coins suspended in white space. These images are effective because they emphasize the subject without giving it any distracting context — but they're also so commonplace that they are themselves a kind of cliché.
DO look for alternate angles
The images you choose for your site don't just say what they appear to say — they also tell the story of the company you're building the site for. A conservative, literal-minded company deserves very straightforward, obvious images. But most companies that are jumping into the web market these days aren't conservative or literal-minded — they're edgy, they're creative, and they deserve the extra effort it takes to find a different angle on an old subject. In your pursuit of alternate angles, consider also throwing some stock videos into the mix. Video is more engaging to the audience, and stock videos offer a way to create some compelling footage even while operating on a limited budget.
DON'T overcrowd your webpage
Not only are visually-cluttered web pages hard for visitors to mentally process, they're also royally difficult to design responsively. Stick to only those images that actually help improve a visitor's ability to comprehend, use, and enjoy the site, and let the rest be white space if necessary. Fewer images mean less clutter and an easier time achieving visual consistency.
DO things the way that feels right to you
Too many people fall into the trap of assuming that, because something is called a 'stock' image, it has to be used in a 'stock' way. Instead, look for alternative interpretations of stock images. Flip them on their horizontal axis and see how that changes the mood. Tilt them seven degrees counterclockwise. Put them outside of the edges of your content panel. There's no reason to follow the rules with a photo just because you bought it from a website that sells them by the thousands. Keep things just a single hair off-kilter, and you can put stock photos to non-stock uses that will keep your sites fresh and engaging.