how to search in n element elastic-search-dsl

Question

I've a problem in elastic search to know if an element already exist, because for a lot of practical reason I store in elastic-search meta data of image for each user (the author) and to avoid some attack I need to be sure that the image hasn't be already saved. here is a standard json file :

{
"user_group": "user",
"user_data": {
    "name": "myname"
},
"user_image": [
    {
        "size": "1920x1080",
        "location": "my_city",
        "description": "my_desc",
        "name": "myname",
        "md5_checksum_image": "a_md5"
    },
    {
        "size": "1920x1080",
        "location": "my_city",
        "description": "my_desc",
        "name": "myothername",
        "md5_checksum_image": "a_md5"
    }
  ]
}

my problem is that I could have thousand of image so ho could I test with a query if I've already registered this image by looking at the checksum ?