For many people photography may be important and to others not so much. In my honest opinion if there is going to be photography in an ad or any creative marketing piece it better be crisp, clear and convey a feeling or message you want or you better just leave it out.
I would like to start off explaining what is bad imagery so you will know what not to use. First do not simply go to google and type in what image you are looking for and see all the wonderful things that appear on the screen and just pick from those. For one thing most of the images will be for web only and too low of a resolution to use in print. More importantly these images may be copyrighted and using them in your work could cost you thousands of dollars if there is a law suit. Not good. Also only use photos taken by yourself if it is very specific and with a good camera.
Photos that are good to use is stock photography when needed but I find it is best to use specific imagery for your situation. If you have a good camera and can take the photos yourself that would be great. Let’s say you are a dental office with new equipment you would want to show that off in your office not just an image from the manufacturer. It will make for a better presentation. Also, using stock images from a reputable site like istockphoto.com or shutterstock.com. These may cost a little but the images will be quality and there are tons to choose from.
The bottom line is that photos can make or break a site and you want to make sure that if you are getting images off the web that you are not violating any copyright laws. For the best results have a professional take some photos or if you want generic images use a reputable stock photography site. Any designer you are working with should be able to help you with this.