How: Cut the images on multiple A4 pages

The HorizontalResolution and VerticalResolution properties contain the resolution in DPI of that Image object. Wifth and Height will give you the actual size in pixels. It is simple to calculate how many pixels represent a centimeter. At that point you can define the rectangle that equals to an A4 sheet. You can use Bitmap.Clone[^] to extract the tiles.
Just a note: if you want all this to print in tiles, you should care about the non-printable margins and of the overlap.