On the web, a floated element is taken out of flow and following text wraps around it (due to the line boxes of the following text becoming shortened). Therefore, you only have the option to float a thing to the left or right. In print, however, you often need to float items to specific places on the page. For example, by floating an element to the top or bottom of a page. When creating a printed document, you define the size of your pages by using the @page rule.
The CSS Specification that deals with this behavior is called Page Floats. Your image would display in the normal flow of the content — just as on the web — except that the content is fragmented into pages. When the page with the image is encountered, the image is moved out of the normal flow and floated to the top of the page where it appears on. (Content that would have been above the image will display below it and normal flow resumes.)