<img src="https://picsum.photos/id/593/400/400" alt="tiger" class="tri alt">
<img src="https://picsum.photos/id/177/400/400" alt="a random traveler" class="tri">

@property --r {
  syntax: "<length>";
  initial-value: 0px;
  inherits: true;
}

.tri {
  --r: 85px; /* the radius */
 
  width: 300px;
  aspect-ratio: 1/cos(30deg);
  --_g:calc(tan(60deg)*var(--r)) bottom var(--r),#000 98%,#0000 101%;
  -webkit-mask:
    conic-gradient(from -30deg at 50% calc(200% - 3*var(--r)/2),#000 60deg,#0000 0)
     0 100%/100% calc(100% - 3*var(--r)/2) no-repeat,
    radial-gradient(var(--r) at 50% calc(2*var(--r)),#000 98%,#0000 101%),
    radial-gradient(var(--r) at left  var(--_g)),
    radial-gradient(var(--r) at right var(--_g));
  clip-path: polygon(50% 0,100% 100%,0 100%);
  transition: --r .6s;
  cursor: pointer;
}

/* the opposite direction */
.alt {
  --_g:calc(tan(60deg)*var(--r)) top var(--r),#000 98%,#0000 101%;
  -webkit-mask:
    conic-gradient(from 150deg at 50% calc(3*var(--r)/2 - 100%),#000 60deg,#0000 0)
     0 0/100% calc(100% - 3*var(--r)/2) no-repeat,
    radial-gradient(var(--r) at 50% calc(100% - 2*var(--r)),#000 98%,#0000 101%),
    radial-gradient(var(--r) at left  var(--_g)),
    radial-gradient(var(--r) at right var(--_g));
  clip-path: polygon(50% 100%,100% 0,0 0);
}

img:hover {
  --r: 10px;
}


img {
  object-fit: cover;
}

img + img {
   margin-left: -80px;
}


body {
  margin: 0;
  min-height: 100vh;
  display: grid;
  place-content: center;
  grid-auto-flow: column;
  background: radial-gradient(circle,#8A9B0F,#9DE0AD);
}