With the Simple Download option, you can buy any image of the specified resolution in your plan (1000px, 800px, or 700px). This plan is created for users who are looking to buy a large number of standard-resolution images, this is an excellent choice for web publishing without a daily time frame restrictions.
Credits option allow you to purchase individual images at any resolution with a significant discount. The discount is possible because you are buying a bundle of images in advance. You may use purchased credits for a year to buy high-resolution images (vector formats included when available) at a 50% discount AND standard-resolution images as well. If you are planning to purchase more than five high-resolution images – this option is for you.