Created a svg polygon triangle, now the question arose how to align it correctly in the center of the image?
img { max-width: 100%; clip-path: url(#clipping); } <img src="https://image.freepik.com/free-photo/shiny-night-city_1127-8.jpg" alt=""> <svg> <defs> <clipPath id="clipping"> <polygon points="0 0,300 0,150 300"> </polygon> </clipPath> </defs> </svg> At the output we get the following: 
Ideally, set in% the position of the triangle relative to the image, for example, in the center - 50% 50%.