This paper presents the comparison of four different mono camera-based steady obstacle position and size estimation algorithms focusing on automatic emergency braking application. Three methods are well known in the automotive field, the fourth is the author's own method successfully applied in aerospace until now. The first contribution is the extension of all methods to consider multiple data points and variable velocity (where possible). The second contribution is an extensive simulation testing of the methods considering constant and variable speeds, attitude uncertainties and the braking characteristic of real vehicles. The methods are evaluated basedon the worst case hitting speed of the obstacle and the precision of obstacle side distance and size estimation. The maximum speeds of applicability are determined for all methods and the results are commented in detail.