I'll post how I was able to do what you're asking. For your application, there may be a slight difference because you are using a picture rather than a plot in your big UIAxes, but this should get you 95% of the way there.
% Window button motion function: UIFigure
function UIFigureWindowButtonMotion(app, event)
PointerLocation = get(app.UIFigure,'CurrentPoint'); %location of pointer
axisYcoords = [app.UIAxes.InnerPosition(2),...
app.UIAxes.InnerPosition(2) + app.UIAxes.InnerPosition(4)]; %UIAxes y coordinates
axisXcoords = [app.UIAxes.InnerPosition(1),...
app.UIAxes.InnerPosition(1) + app.UIAxes.InnerPosition(3)]; %UIAxes x coordinates
%if statement basically asking if you're pointing inside the UIAxes
%InnerPosition and also asks if there is data in the UIAxes. You're
%using a picture so that may need to be updated for you
if PointerLocation(1) > axisXcoords(1) &&...
PointerLocation(1) < axisXcoords(2) &&...
PointerLocation(2) > axisYcoords(1) &&...
PointerLocation(2) < axisYcoords(2) &&...
~isempty(app.UIAxes.Children)
ZoomMag = 10; %zoom magnification
xCalibrate = (app.UIAxes.XLim(2) - app.UIAxes.XLim(1))/...
app.UIAxes.InnerPosition(3); %x value per UIAxes inner pixel
yCalibrate = (app.UIAxes.YLim(2) - app.UIAxes.YLim(1))/...
app.UIAxes.InnerPosition(4); %y value per UIAxes inner pixel
%find what your x and y value are at your cursor within the UIAxes
xValue = xCalibrate*(PointerLocation(1)-app.UIAxes.InnerPosition(1));
yValue = yCalibrate*(PointerLocation(2)-app.UIAxes.InnerPosition(2));
%need to get original data
xData = app.UIAxes.Children.XData;
yData = app.UIAxes.Children.YData;
%plot the pointer location as a black x and plot the original data
%on UIAxes2
plot(app.UIAxes2,...
xValue,yValue,'xk',...
xData,yData,'-o')
%adjust the x and y limits on UIAxes2
xlim(app.UIAxes2,...
[xValue - (app.UIAxes.XLim(2) - app.UIAxes.XLim(1))/ZoomMag,...
xValue + (app.UIAxes.XLim(2) - app.UIAxes.XLim(1))/ZoomMag])
ylim(app.UIAxes2,...
[yValue - (app.UIAxes.YLim(2) - app.UIAxes.YLim(1))/ZoomMag,...
yValue + (app.UIAxes.YLim(2) - app.UIAxes.YLim(1))/ZoomMag])
end
end
