ask: how do I insert an image (background) on the axes and draw on it (background)? here the code:

function userDraw(handles)
    %F=figure;
    %setptr(F,'eraser'); %a custom cursor just for fun
    A=axes;
    % axesUserDraw is tag of my axes
    set(A,'buttondownfcn',@start_pencil)

function start_pencil(src,eventdata)
    coords=get(src,'currentpoint');
    %since this is the axes callback, src=gca
    x=coords(1,1,1);
    y=coords(1,2,1);
    r=line(x, y, 'color', [0 .5 1], 'LineWidth', 2, 'hittest', 'off');
    %turning     hittset off allows you to draw new lines that start on top of an existing line.
    set(gcf,'windowbuttonmotionfcn',{@continue_pencil,r})
    set(gcf,'windowbuttonupfcn',@done_pencil)

function continue_pencil(src,eventdata,r)
    %Note: src is now the figure handle, not the axes, so we need to use gca.
    coords=get(gca,'currentpoint'); %this updates every time i move the mouse
    x=coords(1,1,1);
    y=coords(1,2,1);
    %get the line's existing coordinates and append the new ones.
    lastx=get(r,'xdata');
    lasty=get(r,'ydata');
    newx=[lastx x];
    newy=[lasty y];
    set(r,'xdata',newx,'ydata',newy);

function done_pencil(src,evendata)
    %all this funciton does is turn the motion function off
    set(gcf,'windowbuttonmotionfcn','')
    set(gcf,'windowbuttonupfcn','')