Here is an example of one sign I am working on now. The first image shows the whole line of type. The letters all appear consistent but they are not. Notice in the third image I dragged the 2nd A over to the first A. They are quite different even though they are both from the same image. The leftmost A is smaller in the photo of the sign
This is from a photo taken of a sign
You don't use the photograph for the final artwork, ONLY for a guide for general placement etc.
Place a scaled photograph on the bottom layer on you vector artwork, dim the image to 50%, now in separate layers above the photograph, you create the true vector artwork, doesn't matter if the "A's" are different, just don't use the ones in the photo, use fonts converted to outline as they are or modify them to match you fonts in the photo, again only use the photo a guide.
Also, I always take my photographs straight on center left to right, and center from top to bottom and shoot with a LONG lens, any lens longer than 50mm equivalent in a 35mm format will have much less distortion then other lenses, I like to use 85mm to 105mm.