I am trying to develop an algorithm, but I barely can describe it so I'm not sure what to look for. I have two images img_A and img_B. img_A is the original, while img_B is an image of the same item but slightly different. Let's say one is a photo of a person, while the other is a drawing of that same person. This means that img_B is very similar, to img_A, but it could be slightly rotated and maybe a bit bigger/smaller.
What I am trying to do is : from a point from img_A a_a get the corresponding a_b on the img_B. I think I need to define two points on img_A and their correspoinding points on img_B to define the axis correspondance. Once I have those 4 points, I calculate a_b. The 4 "axis points" will be defined by hand once, then the User will select a point "a_a" by hand and the correspoinding "a_b" will be calculated.
On a visual example: I select the center of the left eye and the lower point of the chin from both images. I then select the right eye from img_A and as a result I get the coordinates of a_b. (if the drawing was perfectly done, the coordinate of a_b will correspond to the right eye on img_b).
How I develop this? I need a matrix to multiply a_a to obtain a_b? how?