Generated by SassMeister.com.

SassMeister-input-HTML.html

<div class="block">
  hello
</div>
<div class="block2">
  hello
</div>

SassMeister-input.scss

// ----
// Sass (v3.3.14)
// Compass (v1.0.0.rc.1)
// ----

@mixin image-replacement(
  $color: transparent,
  $repeat: no-repeat,
  $position: center center,
  $path: null,
  $size: 0 0
) {
  width:  auto;
  height: auto;
  font: 0/0 a;
  line-height: 0;
  text-shadow: none;
  color: transparent;

  &:after {
    content: '';
    display: block;
    @if $path != null {
      background: $color url($path) $repeat $position;
      background-size: $size;
    }
    @else {
      @content
    }
  }
}

.block2 {
  @include image-replacement(
    $path: "/path/to.png"
  )
}

.block {
  @include image-replacement {
    background: red;
    width:  100px;
    height: 100px;
  }
}

SassMeister-output.css

.block2 {
  width: auto;
  height: auto;
  font: 0/0 a;
  line-height: 0;
  text-shadow: none;
  color: transparent;
}
.block2:after {
  content: '';
  display: block;
  background: transparent url("/path/to.png") no-repeat center center;
  background-size: 0 0;
}

.block {
  width: auto;
  height: auto;
  font: 0/0 a;
  line-height: 0;
  text-shadow: none;
  color: transparent;
}
.block:after {
  content: '';
  display: block;
  background: red;
  width: 100px;
  height: 100px;
}

SassMeister-rendered.html

<div class="block">
  hello
</div>
<div class="block2">
  hello
</div>