1. A feature detection apparatus comprising: an input unit, wherein the input unit is capable of receiving (i) at least two unconnected area indicator lines for defining in a digital image an area of interest comprising an object feature, where every two adjacent area indicator lines bound at least a portion of the object feature and at least one of every two adjacent area indicator lines intersects the object feature, and (ii) information identifying a parametric shape that approximates a shape of the object feature in the area of interest; a parameter range defining unit, wherein the parameter range defining unit is capable of defining ranges of parameter values, using a processor, for each of at least two parameters that define properties of the parametric shape, where the ranges of parameter values for each of the at least two parameters define the parametric shape so that the parametric shape intersects at least one of the area indicator lines; a detection unit, wherein the detection unit is capable of detecting object feature pixels in the digital image corresponding to the object feature in the area of interest; a parameter selection unit, wherein the parameter selection unit is capable of selecting a combination of values from the ranges of parameter values, using the processor, that provide an approximation of the parametric shape to the object feature in the area of interest, the combination of values selected by calculating a deviation between the parametric shape based on the combination of parameter values and the object feature pixels; and an output unit, wherein the output unit is capable of providing the parametric shape based on said combination of values for display in the digital image approximately overlying the object feature.