Do you have some sort of model for the fruit?  Maybe an OBJ or STL?  If so, there are some functions available for download from the Mathworks website to important those files.  From there, you will have lists of the faces and vertices.  It the fruit is oriented correctly, all you have to do is calculate the distance between the extreme most points.

Dear Dr. Raymond Rumpf,

Thank you.

Does it requires three-dimensional images?

Please if it is possible more guidance.

I need to know what you are starring with.  How are you storing the fruit in memory to begin with?

I would like that obtain the width, length and depth of an fruit(apple, orange and etc.) using image processing.

Hi. Sorry, I with this theme am not engaged.

Dear Dr. Shafagat Mahmudova,

Thank you.