Stock photos can basically be classed as royalty-free and rights-managed images. You will also have to keep in mind if you want your images to be exclusive or none exclusive. Here are a few terms that will be thrown around 

Royalty free (RF) - images have a single download fee per customer which then grants them the permission to use the image as many times as they want (according to their agreement). They are a lot more affordable than RM but will be downloaded a lot more frequently and may be seen all over the internet.

Rights managed (RM) - images are sold for variable amounts based on how they are intended to be used, the size of the image ad ho log the are intended to be used for. The sell less often but but for a larger amount of money. Its a benefit for the client to have an image that not many other people have used
 
Exclusive � Uploaded to one stock website only and cannot be sold elsewhere unless you request to remove it from the site. Your images can still be sold as art prints and through your own website, just not on other stock websites.

Macrostock � The traditional way of selling stock photos. Generally aimed at professional level photographers with professional kit. You can earn between $30 � $3000 per image depending on the usage and exclusivity of the image and website. Less regular sales than microstock.   

None Exclusive � Upload to any number of microstock websites. Variable commissions per photo per stock site but these are explained to you when you sign up. A lot of sites increase your rate when you have hit a certain amount of downloads. Your cut from Shutterstock, for example, will start at $0.25 and then increase to $0.33 after $500 worth of images has been sold. You a eventually earn up to $0.38 This might not sound a lot but when you have reached that amount you will be selling a lot of photos each day. These prices apply to subscription based sales. One off or enhanced photo sales can earn you up to $28 a time.

Microstock � Some professional photographers may look down their noses at microstock photographers as they feel like they are being priced out of the market. Why hire a professional for �500 when you have so much choice online for just $1 an image? Obviously there is a huge benefit to hiring a professional for a custom job, But as microstock websites are growing at such a rate you just need to adapt and grow with them. None exclusive images can earn you as low as $0.15 a download but the point of microstock is to have a large portfolio and sell a lot of images every day.

Midstock � Typically microstock websites that offer premium rates To become a stock photographer you have to get over the fact that you may only receive about $0.25 (or less!) for the download of a high resolution image. The person buying your photo may have spent several hundred dollars on a subscription to the stock website letting them download a large amount of images per month.

Source - Microstock Diaries www.microstockdiaries.com

Good luck