Rectangles bleeding out of axes when zooming

In a GUI I'm developing I have a panel then a child axes in it. In this axes I 'imshow' a given image. After some calculations I have several coordinates that correspond to areas in the image and I draw them over the image in the form of squares, using the 'rectangle' function. The problem is, when I zoom in on that axes with the overlayed rectangles they bleed out of the axes and into the other areas of the GUI. How do I prevent this from happening?

Thanks in advance.