I don't know if this will help but if I try to resize a photo in photoshop irrespective of its original size.
I firstly open the source photo. Then
I create a new template (file, new) and set the dimensions to the size I want, just say passport photo (2" x 1.5") and set the resolution to say 300 ppi with a transparent background.
I now have two documents open.
I then drag a copy of the source photo to the target document (it might look enormous) and then close the source photo.
Then using "Image Transform" I resize the document (make sure you maintain proportions, there's more than one way of doing it) by pushing and pulling it over the template size, that way you might have bits and pieces that you don't want outside the template area.
Then click on the layer, Ctrl+A, which will put moving ants around the bounds of your new photo (2 x 1.5) and then Image Crop.
I know you are going to use another program but the principle should be the same. I've just produced my Indian Visa application photos and it worked for me.
Just hope I haven't taught you how to suck eggs?
