Change color of text responding to background color

Answer 1

Another solution could be to make your image darker.

.infobox {
  width: 110mm;
  height: 65mm;
  background-image:url(https://i.pinimg.com/564x/86/70/f2/8670f2ab34bf4082bf3cef004aae0826.jpg);
  background-size: cover;
  position: relative;
}

.infobox:before {
  content: '';
  position: absolute;
  top: 0; right: 0; bottom: 0; left: 0;
  background: rgba(0, 0, 0, 0.4);
}

.text {
  position: absolute; bottom: 0; 
  text-align: center; color: white;
}

<div class="infobox">
  <span class="text">Lorem ipsum dolor sit amet, consectetur adipiscing elit. Morbi vel quam in enim pulvinar fringilla. Etiam molestie convallis pharetra. Sed et tortor tortor. Vestibulum ligula ex, rhoncus semper metus ut, hendrerit porttitor risus. Quisque at porta magna. Phasellus vel vulputate diam. Maecenas sem est, aliquet nec odio euismod, posuere luctus nisl. Vestibulum posuere iaculis massa, sed cursus dui pellentesque sed.</span>
</div>

Answer 2

You may simply add a text-shadow with a dark color and you will have a better rendring whataver the image you will use:

.infobox {
    width: 110mm;
    height: 65mm;
    background:
    linear-gradient(to bottom,transparent,#fff),
    url(https://i.pinimg.com/564x/86/70/f2/8670f2ab34bf4082bf3cef004aae0826.jpg);
  background-size: cover;
  position: relative;
}

.text {
  position: absolute; bottom: 0; 
  text-align: center; color: white;
  text-shadow: -1px 0 1px #000,
               1px 0 1px #000,
               1px 1px 1px #000,
               -1px -1px 1px #000,
               0 1px 1px #000,
               0 -1px 1px #000;
}

<div class="infobox">
  <span class="text">Lorem ipsum dolor sit amet, consectetur adipiscing elit. Morbi vel quam in enim pulvinar fringilla. Etiam molestie convallis pharetra. Sed et tortor tortor. Vestibulum ligula ex, rhoncus semper metus ut, hendrerit porttitor risus. Quisque at porta magna. Phasellus vel vulputate diam. Maecenas sem est, aliquet nec odio euismod, posuere luctus nisl. Vestibulum posuere iaculis massa, sed cursus dui pellentesque sed.</span>
</div>