You may think you did a flawless job zooming and cropping, but it's still obvious that you're standing in a bar with your friends (and you've probably had a few cocktails). Is that the first impression you want to make on your clients, colleagues, or future boss?

There are universal keys to pulling off a professional, competent looking photograph, says Ann Pierce, co-founder and CEO of PhotoFeeler, a site that allows you to upload headshots and receive feedback on your likeability, influence, and capability.

Based on a study of roughly 60,000 photo ratings, Pierce has distilled the elements of the ideal LinkedIn photo. She and Nicole Williams, LinkedIn's in-house career expert, share their five best tips. [Tweet these tips!]

1. Make your background work. You're better off contextualizing your photo background with something related to your business, Williams advises. If you're a chef, take your shot in a kitchen. If you're a sales executive, head for the boardroom. "Look at LinkedIn profile photos of successful, influential people in your industry," Williams suggests. "That'll give you a good idea of what you should be going for."

2. Enlarge your pupils. It sounds weird, but Pierce says, "Our pupils naturally widen in regularly lit settings when we're happy or with someone we like." A camera flash or artificial photo lighting tends to shrink your pupils, which will make your smile or enthusiasm seem put on, she adds. She recommends using a program like Adobe Photoshop or PicMonkey to touch up your pupils. (Just don't overdo it, or you'll look like a cartoon character.)

3. Dress the part. This is by far the most effective way to look competent and influential, Pierce stresses. "A simple black or gray blazer can do wonders," she says. "Even a button-down blouse with some bright accessories will get you most of the way." But again, consider your industry, Williams advises. If you're an anthropologist or a personal trainer, you'll want your attire to reflect what you do, she adds.

4. Tweak the contrast. "Adding a bit of contrast generally makes photos look more professional," says Pierce.

5. Opt for color. Unlike black-and-white photos, color communicates life and vitality, Williams explains. "Black and white can feel dated," she says. "It can also age you, so it's especially bad if you're an older employee."