Images, including photographs and graphic elements, may be the most important thing on your web site. People respond to images more readily than they do to lines of text. They will help create a mood for your site, and what they convey will be what people take away when they leave your site.
With that in mind, you should pay attention to the following when selecting images:
Every photo tells a story. Are your images telling the stories you want them to tell? If you’re not sure, ask people to view your site and let you know what they are feeling from seeing your photos. If you have a photo of a group of people sitting around a table, that doesn’t say much (it could represent anything). So try to use photos whose stories are immediately relevant to your content. Details often speak loudest. Maybe the objects on the table would say more than the people sitting around it. A photo doesn’t have to speak volumes, just a clear phrase.
Photos have color, composition, and movement. Do the colors in your photos blend well with the site’s color palette? Does the composition of the photo lend itself to the mood of your site? Does any movement in the photo elicit an emotional response, or feeling, that supports the site?
If you have humans in your photos, do they offer a fair representation of whom you are trying to attract to your site? Are they biased in any way, or do they suggest bias? In which direction are they looking? Do their eyes point inward, to more of the site, or to its edges, away from it?
How many photos are on a page? Do they compete with one another, and cancel one another out? Or do they harmonize well?
The web doesn’t require high resolution images, but they should not look pixelated or out of focus. If you start with an image of at least 1MB, it should be OK. If not sure, start with higher res; you can always bring it down.
Make sure your photos meet the aspect ratio of the box that will house them (for instance, 4:3 or 2:3). You can crop photos to meet this. Make sure you select photos that will actually work for that aspect ratio. If you can’t crop a landscape (horizontal) photo to be in a portrait (vertical) box, then don’t use it.
Beware of using “effects” such as those offered by Photoshop. More often than not they will make your site appear amateurish. If you have professional-quality photos you don’t need to dress them up.