Because an image of a shrimp
represents a two-dimensional projection of a three-dimensional
object, the pixel area should be approximately proportional to
the square of the one-dimensional carapace length, if the
shape does not vary too much with carapace length. From an
image analysis perspective, the challenge is to differentiate
shrimp in an image from the background, as well as from
each other. Because shrimp are red, they can be differentiated
using a background of another colour, then applying intensity
thresholding (Russ, 1992).