span.foo img {
        padding: 0px;
        margin: 0px;
}

span.foo {
        border: 1px solid #000000;
}


        <table>
        <thead>
                <tr>
                        <th><span class="foo"><img src="a"><img src="b"><img src="c"></span></th>
                        <th>bar/th><th>sdfsdf</th>


                </tr>
        </thead><tr>
                        <td colspan="3">dfgfd</td>
                </tr>

        </table>