Try changing lines 280 - 282 in /wp-content/themes/[your_theme]/lib/functions/image.php from this,
$out .= '<a href="' . esc_url( $link_to ) . '" rel="prettyPhoto">';
$out .= '<img alt="" src="' . esc_url( THEME_IMAGES . '/shortcodes/transparent.gif' ) . '" style="height:' .
esc_attr( $height-10 ) . 'px;width:' . esc_attr( $width-10 ) . 'px;" class="transparent_border">';
To this,
$out .= '<a href="' . esc_url( $link_to ) . '" rel="prettyPhoto" title="' . $title . '"' .'>';
$out .= '<img alt="'.$alt.'" src="' . esc_url( THEME_IMAGES . '/shortcodes/transparent.gif' ) . '" style="height:' .
esc_attr( $height-10 ) . 'px;width:' . esc_attr( $width-10 ) . 'px;" class="transparent_border">';