Successfully complete the indicated game to unlock the corresponding gallery.

Art Gallery 1: Metal Slug
Art Gallery 2: Metal Slug 2
Art Gallery 3: Metal Slug X
Art Gallery 4: Metal Slug 3
Art Gallery 5: Metal Slug 4
Art Gallery 6: Metal Slug 5
Art Gallery 7: Metal Slug 6
Tonko Gallery: All seven Metal Slug games under the Easy difficulty setting and limited continues.