Coppermine can be used both as a monolithic gallery for just you (as admin) or as a community gallery. Different level of user interaction are possible. One feature that you can use to improve user experience is allowing your visitors to comment the files in your gallery.
Coppermine has different levels of permissions for visitors to post comments: you can assign the permission to post comments based on groups membership. By default, coppermine has the groups "administrators", "registered", "banned" and "guests". The guest group applies to visitors of your gallery who have not logged in.
You can assign the permissions to post comments for particular groups on the group control panel. By default, registered users are allowed to post comments, anonymous users (guests) are not allowed to. You're welcome to change this, but you should keep in mind that allowing comments for anybody might result in attracking spammers to your page.
If you have disabled anonymous (guest) access by setting "Allow unlogged users (guest or anonymous) access" to "no" in Coppermine's config, you don't have to worry about the guest group at all: since they are not able to access individual pics, they can't post comments no matter what.
The above mentioned group settings are just a general switch that determines if a visitor can post comments at all. You can fine-tune this setting on a per-album page: on the album's properties page you can switch off comments for particular albums. Even if a user belongs to a group that is allowed to post comments, he won't be able to post comments in albums where you have set "Visitors can post comments" turned off.
There are several options in Coppermine's config where you can fine-tune the behaviour of comments. It is advisable that you change only one option at a time and then test the impact the option has on your gallery.
In the past few years, comment spam has started to become a problem. Spam is unsolicited, undesired bulk messages that orginally became an issue in emails. Recently, spammers started using techniques to flood web pages that allow users to interact by posting comments, mostly on blogs and forums, but an increasing number is reported for coppermine as well.
There are basically two types of spam messages: those that get posted by a human spammer who vists your page and just pastes his unwanted messages into the input field and submits the form, and those that use a so-called "bot" (a script run on a remote computer that automatically scans the pages that allow comments and subsequently fills in the fields and submits them automatically). It's hard to fight spam posted by actual humans, as all methods to make it harder for them to post their spam messages will make it harder for your regular, legitimate users as well. However, it's easier to fight the spam messages posted by bots: you just need to make it mandatory to do something only humans can do, but automated scripts can't.
One of the things scripts currently can not do is reading scrambled text on images and entering the text into an input field. Images that show random, scrambled text are being called "captchas" - that's why a visual confirmation (captcha) option was added to coppermine in cpg1.5.x. There are reports though that spammers managed to break captcha-authentication using OCR or just social engineering (they display the captcha on another page and ask human visitors of that page to spell the captcha for them - as a reward, those users get access to something they want, e.g. a free porn pic download). This being said, captchas don't represent an ideal protection against comment spammers - it is a matter of time until spammers will manage to break the captchas used by coppermine. Actually, the war against spammers can not be won using technical tricks, as spammers will find methods to overcome the technological barriers. Additionally, captchas might lock out legitimate users (e.g. users with impaired eyesight).
Another option to protect your gallery from being flooded with silly spam messages (most of those messages advertizing online pharmaceutical products) is enabling comment approval: when enabled, all comments posted will not be visible instantly, but require you (as coppermine admin) to approve them first. As a drawback, this will require additional moderation effort from you (the gallery admin).
Another new feature in cpg1.5.x is the option to use the Akismet service: Akismet is a third-party service that evaluates user input (usually comments) and provides feedback if the user input is spam or not. To do this, Akismet provides a huge database of spam samples and compares the submit data to the records they already have in their database.
To use Akismet, you need a valid Akismet API key. To get such a key, you need to sign up (for free) for small/non-profit pages on the Wordpress page to obtain an API key. If you plan to use Akismet on a commercial page, you need to purchase a professional API key on akismet.com/commercial/
After you got your API key by email you can paste it into this config field "Akismet API key". You can not make up the API key, nor can you use someone else's API key.
Leaving that config field empty will disable the usage of Akismet.
After entering your Akismet API key into the corresponding config field, go to the review comments page - at the bottom you will find a little info box that will display the number of comments that Akismet has blocked for you and a lookup field that displays the results of a connection attempt with the Akismet server using your Akismet API.
To determine if Akismet works on your gallery, post a test comment with a user or guest named viagra-test-123 with the comment This is a test comment. If everything works as expected, that comment should be tagged as spam. Depending on the akismet option you chose in config, the comment will be deleted instantly or will be marked as unapproved comment (visit the review comments page to verify that).
In rare cases it might happen that legitimate comments are being tagged as spam comments by akismet - if this happens and you approve such a comment manually on the review comments page, a sample of that comment will be submit to the akismet database as well to help them fine-tune their filters.
Please do not ask questions how to get an API key on the Coppermine support board: both the Wordpress pages as well as Akismet.com provide documentation how to obtain an API key. Go to those pages to get your API key.
The Coppermine dev team is not overly fond of comments at all; we understand that it is something that helps in community-building and is being requested by our users. However, we suggest that you ask yourself: does my gallery really need comments? Is the community I cater for large enough that comments will actually make sense? When in doubt, disable comments from anonymous visitors, or disable comments completely.
On the "Review comments" page the admin can list all comments posted and sort them by different criteria. You can mark comments approved or unapproved, and you can also delete comments.
When logged in as admin and browsing an individual file (intermediate image), you will see three icons next to comments: