Actually you can use simple CSS with styling extensions like Stylus to achieve similar effect.

    .ind img {
        height: 100%;
        border-right: 3px solid red;
    }

If you want different color for different level of indent, just use attribute selector, like:

    .ind img {
        height: 100%;
        border-right: 3px solid;
    }
    img[width="40"] {
        border-color: red;
    }
    img[width="80"] {
        border-color: blue;
    }