Question: I am new here, I have generated 5 images from an array. Now I want to select those images as we select using checkbox (means i can select 1 image or 2 image or more as per choice). After selecting I want to display their name as an alert that you have selected these images. Please guide me because i am new in javascript. Thanks in advance.

Answer: 
You can specify the specific users & SSH keys to use for an instance by setting the instance level [`sshKeys` metadata key](https://developers.google.com/compute/docs/instances?hl=en#sshkeys). You can also do this from the command line using gcutil's `--authorized_ssh_keys` option:

```
$ gcutil addinstance --authorized_ssh_keys=username1:/path/to/keyfile1,username2:/path/to/keyfile2,...

```

If you want to make sure that no instances get the full set of users/keys, you can remove the `sshKeys` project level metadata key. From the Console, click `Compute Engine`, then `Metadata`, then click the trash can icon next to the `sshKeys` key. You will then *need* to specify keys for each instance, or you will not be able to log in at all. (which may be what you want in a fully automated environment)

Note: Running `gcutil ssh` will generate a key-pair (if needed) and add it to the `sshKeys` key.
Google adds these ssh keys to the project ssh-keys automatically. So you need to block project-wide SSH keys: <https://cloud.google.com/compute/docs/instances/adding-removing-ssh-keys#block-project-keys>

You can do it via meta-data:

`"block-project-ssh-keys": "true"`