Resizing a picture by dragging one of the side handles will change the aspect ration of the image, making it appear stretched unless this is intentional resize the picture by dragging one of the corner handles.

To resize a picture to some precise height or width, right-click on it and choose properties from the pop up menu, then select the Appearance tab and check 'Specify Size, enter the height of width of the image in pixels or as a percentage of the original size. You can also increase
the horizontal or vertical spacing around a picture if you find your text or other content is lying too close to the picture.