Pictures can help bring to life a lengthy article, a boring blog post or a social networking profile. They enhance the reading experience, and search engines value them. A written piece with an image will rank higher than a similar one without an image. For this reason, online stock photo sites purchase photos of all kinds for pay. If photography is your talent, then you could earn cash each time your picture is downloaded. Buyers may also pay you upfront for your images.

iStockphoto

One of the leading online stock photo sites is iStockphoto.com. You have to sign up for a free membership before you can contribute photographs. Then, you can apply to become a contributor, which consists of reading a manual and taking a quiz. As part of the application process, you'll also have to submit three samples. If accepted, you can earn a base royalty rate of 15 percent. If you decide to become an exclusive contributor, the rate is 22 percent to 45 percent. Not anyone can become an exclusive contributor. You need 250 downloads and your approval rating has to be at least 50 percent. The approval rating is not relevant if you reach 500 downloads. Keep in mind that you have to reach $100 in commissions before you can submit a payment request to get paid.

Dreamstime

Another popular online photo stock site with its own application process is Dreamstime.com.  You have to become a member first, upload initial images and submit your application. It offers suggestions for ways to improve your work if your application is denied. You can make changes and re-upload photographs. You'll start at a base level, and as your downloads increase, you can sell at higher levels for higher prices. The pay rate is 30 to 50 percent.  You can become an exclusive photographer for the site and get paid 60 percent plus $0.20 per approved photo. Another option is to submit exclusive photos for 30 to 50 percent plus an additional 10 percent bonus.

Shutterstock

Shutterstock.com pays you a commission every time one of the images you submit is downloaded. It's free to sign up, and you can remove any of the images you upload at any time. The best part is that you keep the rights to all of your photos. If you choose to use it or sell it elsewhere, you have that option. The pay is $0.25 to $28. Keep in mind, though, that you won't get a payout until your commissions reach $75. Once you reach $500, your commission will increase, and again around $3,000. If you're interested in Shutterstock, you have to submit 10 images for review. Once at least seven of them are accepted, you can start selling. If three or more fail to pass the initial review, you can wait 30 days and try again.

Flickr

Free sharing sites allow web owners, writers and other content products to use images for free based on a Creative Commons license. The stipulation in many cases is that the photographer gets credit for the work where it's used. One popular site is Flickr.com, owned by Yahoo. You might believe that it's a good way to get exposure but that uploading to Flickr is not a way to earn cash. That's not the case. What's happening is that photographers are being contacted by individuals and companies who want to pay for photos. It's all taking place via email. A company may contact you and ask to pay a usage fee for one of the images you upload. The key is to have a professional body of work represented, and targeted keywords in your tags so that potential buyers can find them. You can also mention in your profile that the photos are available for sale. Become known in the Flickr community to grow your reputation, which will lead to more sales.

The key to success with online photo stock sites is to submit images on a consistent basis. You'll build your reputation online and buyers will trust that they can count on you for quality work. Who knows? Getting paid for your images might translate into full time work down the road.