All images on any web server have to be uploaded and stored on the server somewhere. Images are never actually uploaded to a 'page'. They are uploaded someplace and then 'linked' to on pages.
The same applies for Doodlekit. You have to upload your images to an album first before you can link to them on a page. You can create as many albums as you want. You can also 'hide' an album so that only you can see it when logged in. You might want to do this for images you want to insert into pages but don't want a visible album showing for.
