This infographic Guide to Pinterest images by Josh Davis is a simple and quick guide to getting the right sizes and formats to effectively pin your images from your website.
The old way of preparing images on websites probably would need to be changed as there are proper formats for images to be visually effective in the Pinterest profiles.
There are 2 ways for images to appear in Pinterest. The first one is the image would appear a pin in the pinboard. This is normally small in size. The second way is when this pin is clicked. The image would be enlarged and appeared in a new page. The format of your original image would decide the ways they are appearing in Pinterest.