The rule of the thumb says the more images you have in your portfolio the more images you sell and the higher monthly income you get. Typically, the microstock agencies send you a check or a PayPal transfer if you have earned a certain amount of cash, typically $100. A few agencies (e.g. Pixamba, BigStockPhoto) offer smaller $50 payouts, thus allowing you to get your earnings faster.8)Copyright
Most stock agencies act as your non-exclusive sale agents, offering your royalty free stock images to the content buyers and keeping you as the only copyright owner. Avoid companies that request you transferring your copyright to them or to their buying customers! If you transfer the copyright you loose all the rights for your image ownership.