How to specify skin image path in Knockout HTML template?

You need to call the function into js from the template.

require.toUrl('images/icon-paypal.png');

If you are trying to add just an image path in phtml file, you should follow below way,

<img src="<?php echo $block->getViewFileUrl('images/image.png') ?>">\

To do this with Knockout way:

Try adding a variable to window from *.phtml file:

<script>
  window.imgpath = '<?php echo $block->getViewFileUrl('images/image.png') ?>';
  </script>

and reading that variable from window:

  function someFunction() {
  var imgPath = window.imgpath;
  }

Change your image code :

<img alt="" data-bind="attr: { src: someFunction() } "/>

create js variable in phtml

<script>
  var imgpath = '<?php echo $block->getViewFileUrl('images/image.png') ?>';
</script>

Now create new js function

getImagepaypal: function() {
                return window.imgpath;
            }

in you html file

 <img alt="" data-bind="attr: { src: getImagepaypal() } "/>