An Image Set attribute is similar to an Image Field attribute as is a way to upload an image to the server for your content. The difference, however, is that an Image Set is used to upload multiple sizes of the same image for different uses. An example would be an image upload for a store product. Instead of using the full size image for different purposes throughout the store, an image set can be used to generate a thumbnail sized image and a full sized image for a product listing and a product detail page.
An Image Set has two upload methods. The first is to show individual fields for each different image type, granting the ability to upload each image file individually. The second method is to just show one upload field. In that case the uploaded image will get copied and resized for each image field in the image set. Regardless of the upload method, each image is used the same when used in a content layout or a content template.
An Image Set field is a parent field. You must assign one or more Image Upload fields as child attributes in order for it to be used.
Uploading images individually:
Uploading a single image and having it resize for other images.