AboutPixel

http://www.aboutpixel.com/

AboutPixel is a free online stock photography resource where you can download free stock photos belonging to various categories. To download the stock mages (professional photos are also available), you need to exchange them for credits which the service will grant you on a daily basis (in packs of five credits). The credits you don’t use on a given day will pile up on AboutPixel and you can also obtain more credits by uploading an original image of yours to the portal.

You can use the search field to browse through the stock pictures to find the one that suits your needs. The internal search engine also allows you to refine your search by category, timespan, format and color o the image. All images vary in size and the higher the resolution, the more credits you will need to download them.

StockedPhotos

http://www.stockedphotos.com/

StockedPhotos is a stock photography marketplace for royalty free stock photos. There is a large range of stock photos available, all shot and retouched by professional photographers and featuring professional models.

All stock photos are in high-quality and available in four sizes (small, medium, large, jumbo). To download the royalty free pictures, you need to subscribe to one of the pricing plans (one month-, three month- or one year-long) available as you cannot buy any of the stock photos individually.

AskPhotos.com

http://www.askphotos.com/

AskPhotos.com is an online resource for creative professionals who need premium royalty-free stock photos. There is a wide range of image categories and collections you can choose from, spanning from animals to to people, industry or health-related pictures.

All stock photos are in high-quality and available in five sizes (up to 11.52" x 7.68" @ 300 dpi). To download royalty free images, subscribe to one of the monthly pricing plans available and then download all images you need. You can also buy single photos if you prefer.

Deposit Photos

http://depositphotos.com/

Deposit Photos is an open marketplace where you can purchase royalty-free stock photos and vector illustrations for your creative works. Photographers can also contribute their photos and sell them via Deposit Photos storefront .

All images are available in high-resolution and different sizes. You can download your images either by paying a monthly subscription fee or by purchasing credits which you will spend each time you buy an image. You can also get the images you need while on-the-go via text message.

Alamy

http://www.alamy.com/

Alamy is an open marketplace for stock photos. Buyers can find a large collection of rights-managed and royalty free images while photographers have the opportunity to sell their own pictures and make money.

All images are available in high-resolution and different sizes. To refine your search inside Alamy archive you can use the category list on the left sidebar which allows you to find exactly the stock images you need. Alamy is also available on the iPad with a dedicated mobile app.