If you use image as background than add class ".bg-img" in image and add below class in parent.

.ratio_40 - 40%

.ratio_45 - 45%

.ratio2_1 - 50%

.ratio2_3 - 60%

.ratio3_2 - 66.66%

.ratio_landscape - 75%

.ratio_square - 100%

.ratio_asos - 127.77%

.ratio_portrait - 150%

.ratio1_2 - 200%