<p:commandLink> con imagenes

//JSF

<h:commandLink action="#{user.goLoginPage}">
    <h:graphicImage library="images" name="sofa.png" />
</h:commandLink>

Otra manera

<p:commandLink action="#{controlador.editar(registro)}"
                                       oncomplete="wdlgDetalhe.show()"
                                       update=":frmPrincipal:pnlDetalhe">
                            <p:graphicImage url="./resources/imagens/editar.png"
            style="background-color: transparent; vertical-align: middle; border: none"
                                           width="20" height="20"/>
                       </p:commandLink>