A regular TV screen has an aspect ratio of 4:3, that is, if the screen is 4" wide it is 3" tall (4/3=1.3333333333 or 1.33)
An HDTV screen is 16:9, if 16" wide it is 9" tall (16/9=1.777777777777 or 1.78)
An anamorphic DVD "assumes" that you are using an HDTV display that will electronically "squeeze" the image to fit in the 16:9 screen. To preserve the maximum resolution of the DVD, the image is placed on the DVD "stretched". A full explanation of this can be found at the following:
Anamorphic DVD Explanation
Anyway, if you capture the native image from the anamorphic DVD you will get a "stretched" picture. To fixed this you need to use a graphics program that will allow you to "fix" the aspect ratio of the captured picture. Remember that if the original aspect ration of the movie is greater than 16:9 (1.78), you will have black bars at the top and bottom of the screen capture, but don't remove those until you have first corrected the aspect ratio.
Example:
Original screen cap 720x480 (notice oval instead of circle)
Fixed screen cap 720x405 (1.78) notice proper shapes
In the graphics program I changed the image size from 720x480 to 720x405.
