Here we will discuss about how to make sure a core image has the correct DPI. At this point, let's assume that your digital-line-scanner scans the core at 100 dots per centimeter. This is equal to 254 DPI.
The first thing to do is open the image in a program like Adobe Photoshop, or The Gimp. At this point, we will assume that you are working with Photoshop.
In Photoshop, you will want to view the image's properties by going to Image -> Image Size. A dialog will appear showing the image width, height, etc. If the resolution does not match the expected DPI then we will need to change it. Before doing that make sure that the Resample Image checkbox is unchecked. Otherwise, when you change the DPI of the image, the image will get resized. After you uncheck the Resample Image option, edit the Resolution text field and enter the correct DPI. At the time of this writing, most core section images have a DPI of 254.
If you realize that more than one image contains the wrong DPI, you can create a batch process in Photoshop to help you deal with all the images.