Using Images in VSE

I am using Blender’s VSE to make a short video clip, using mainly still images of different sizes.
When I add an image into the sequence editor, I notice that Blender alters the x/y ratio of the image in order to fit the screen format I’ve set up for the preview screen and render settings.
Is there some way of preserving the aspect ratio of the images I use in the VSE?

Create an image in GIMP with the aspect ratio you want you video clip a transparent background. Then put your image on the image. When you load it your image will appear correctly.

or, there is the built-in transform effect that re-scales the image back to the original ratio. I think it fills in the letterbox with black. see

Ok, thanks for your replies shadowbane and PapaSmurf.