If your image borders are not showing as they do in the demo, this is due to a recent Divi update and the fix is simple.

Find this section in the stye.css of the child theme:

/*Add the transparent borders to the images*/

.ds-image-border {
    outline: 5px solid rgba(255, 255, 255, .5);
    outline-offset: -10px;
}

And replace with this:

/*Add the transparent borders to the images*/

.ds-image-border img {
    outline: 5px solid rgba(255, 255, 255, .5);
    outline-offset: -10px;
}