You must have seen on the net that many websites offer money for uploading content to their websites, but it is not the uploading that gives you money, so it does not matter how much content you upload, your earning could be very low. The money you get from these websites are due to the amount of clicks or downloads your content has got. So more the clicks or more the download more will be your income. So you need to choose Paid to Upload sites very carefully and do not sign up on many sites as you might not upload every content to each site. So go for one site only for better results.
Like many websites only allow uploading photos while other may allow every type of file. Similarly one may pay for every click on to image while other may give for downloading the image. So different websites have different criteria for awarding money to its members.
You might also think how these sites get their revenue, so answer lies in the website only. These website has lot of advertisements on every page which ear for them and you are paid only a small bit of that. Many websites also allow you to join their referral network for more members. Not only this many websites offer you to join advertisement network means your content page will have ads from that network and any click on those ads will give you money. Isn't it cool.
Here are some of the Paid to Upload website.