[Quoth]

Have the outer div have CSS in its class to set left & right margins and padding 0 and center

HTML

<div class="centred-stuff">
  <img class="img-1" alt="" src="../Images/img_1.png"/>
  <img class="img-2" alt="" src="../Images/img_2.png"/>
  <img class="img-3" alt="" src="../Images/img_3.png"/>
  <img class="img-4" alt="" src="../Images/img_4.png"/>
</div>

Using <p class="centred-stuff"> (with a closing </p>) can work well instead of div and suit non-heading centred text.

I would use <p>

CSS

.centred-stuff {
   margin-left: 0;
    margin-right: 0;
    padding-left: 0;
    padding-right: 0;
    text-align: center
}

.img-1 {
  height: 100 px;
  width: auto;  /* or exact pixels */
  padding-right: 5px;
}

No padding on the last image on the line. 
If you use "pt" instead of "px" some renderers might change the image size as user changes font size!

You can space images in the one <p> tag using a single space.