Input image strip without stretching to fit output frame When you add an image strip to the Video Sequence Editor, it stretches/shrinks your image to fit the full output frame.

How can I add an image at its original resolution?  For example, if I add a 60x60 pixel image, it should appear very small in the final 1080p render.
The default behaviour of an image strip added to the VSE is to scale to the render resolution set for the blend file. To change this behaviour in the way you have specified; enable "Image Offset" in the Strip Input panel on the properties bar for the selected image sequence, then use the X and Y value inputs to position the image within the output image space. You also want to set the blend type to "Alpha Over" so that the underlying strip is visible.