将div与图像的右边缘对齐

I'm trying to make a button (div with background color) just below an image that aligns with right side of the image. Both are inside a wrapper div. When I float right the button it makes the wrapper div expand and the button goes beyond the right edge of the img. I cannot give the wrapper div a fixed width as it needs to be responsive.I'm trying to make a button (div with backgroun