How to keep the object size constant while it is moving? I need to move an object in depth without automatically changing its size. Is it possible?

Blender automatically scales the object's size when the object is moved in depth according to the principles of perspective. I want to manually control the scaling.
If you  place your pivot point at the camera ( e.g. 3D cursor to camera, then '3D Cursor' selected as pivot center), when you scale your object in all axes (or any element of it, in edit mode,) the shape will not appear to change in perspective, when seen through the camera. If you then want to 'scale the object manually', you can do that in some other space, say, by setting the pivot to 'Median Point'.