If you have several images with, say the same person, then it might be more convenient to select those images, and specify that this person is on all images using the Annotate Multiple Items at a Time.
If you want to annotate a stack of images you can do that when the stack is collapsed. You just need to select the top image of the stack and annotate multiple images. (If you annotate single image, only the selected image, the stack head in this case, is being annotated.) Of course expanding the stack and selecting all images works as well.