gang님 안녕하세요.
적용테마 내 /skin_bs/board/gallery/list.skin.html 파일 15번째 줄쯤 아래 css 소스를 삭제하시면 될거에요.

.board-gallery .gallery-item .gallery-item-image-in:after {content:"";text-align:center;position:absolute;display:block;left:0;top:0;opacity:0;-moz-transition:all 0.2s ease 0s;-webkit-transition:all 0.2s ease 0s;-ms-transition:all 0.2s ease 0s;-o-transition:all 0.2s ease 0s;transition:all 0.2s ease 0s;width:100%;height:100%;background:rgba(0,0,0,0.45)}