Updating an ROI

Hello. This is sort of related to another post so I apologise. I have an image "IM" and want to be able to draw a box, resize and move the box and for the new ROI to be drawn in a second axes component.

J = imadjust(IM,stretchlim(IM),[0 1]);
axes(handles.axes1)
axis off;
imshow(J);
zoom on;

%Get ROI
h = imrect;
p = h.getPosition()
assignin('base','p',round(p))
addNewPositionCallback(h,@(p)assignin('base','p',p));

p1=evalin('base','p')

%Get x & y coordinates
sp(1) = min(floor(p1(1)), floor(p1(2))); %xmin
sp(2) = min(floor(p1(3)), floor(p1(4))); %ymin
sp(3) = max(ceil(p1(1)), ceil(p1(2)));   %xmax
sp(4) = max(ceil(p1(3)), ceil(p1(4)));   %ymax

Zoom = IM(sp(2):sp(4), sp(1): sp(3),:);     % This is the ROI
J = imadjust(Zoom,stretchlim(Zoom),[0 1]);
axes(handles.axes2)
imshow(J);

It works the first time I initialise the box on the raw image but doesn't update as I move and resize the box. Have I missed something? Thanks Jason