[{_id:ObjectId("111111111111111111111111"),images:[{id:ObjectId("123123224454323123121314"),name:"foo",url:"cdn.domain.com/images/foo",topic:"lorem ipsum"},{id:ObjectId("222123224454323123121314"),name:"bar",url:"cdn.domain.com/images/bar",topic:"lorem ipsum"},{id:ObjectId("333323224454323123121314"),name:"baz",url:"cdn.domain.com/images/baz",topic:"lorem ipsum"}]},{_id:ObjectId("222222222222222222222222"),images:[{id:ObjectId("888823224454323123121314"),name:"text",url:"cdn.domain.com/images/text",topic:"lorem ipsum"},{id:ObjectId("999993224454323123121314"),name:"foo",url:"cdn.domain.com/images/pic",topic:"lorem ipsum"}]}]

db.collection.aggregate([{$unwind:"$images"},{$match:{"images.name":{"$regex":"fo*"}}}])