How do I move a picture box in-between multiple forms?

Forms and controls aren't normally shared, and the Location property of any control is relative to the top left corner of the containing control (and Form is derived from Control and is the container for all the form controls).

If you want to actually move a control between two forms, you need to remove it from the containing Form Controls collection, and add it to Controls collection of the new Form:

public static void MoveControlBetweenForms(Control c, Form src, Form dest)
    {
    src.Controls.Remove(c);
    dst.Controls.Add(c);
    }

But ... things may not work as you intended as all the events on the picture box will still be linked to the original form not the new one ...

Me? I'd move the Image from Form to Form and use a separate PictureBox for each instead.