The internet is a bizarre place. I have learned most of what I know about photography through the internet, and without a gathering of faceless names online offering tips and suggestions, I would likely still be taking some pretty mediocre images. Online critiques have helped me grow and learn as a photographer. Being able to give thoughtful critiques to others and well as receive feedback graciously is a valuable skill, and one I think everyone should practice. Taking the time to offer someone a meaningful critique requires you to articulate your own thoughts and feelings, which it turn makes you more aware of what exactly it is you like or don’t like about a photograph which then allows you to emulate those preferences in your own work. Being able to be polite about the process is what makes people respect you instead of hate you.
Here are my three main rules for thoughtful, non-offensive critiques.
1) Don’t be a jerk. This should be obvious. If the only comments you have are negative, you are probably better off not commenting. Even if you don’t particularly like an image, there is always a way to word your feedback considerately if you must offer a critique, such as when judging a contest or specifically asked for one.
2) Offer the Compliment Sandwich: Start with something positive, add thoughtful criticism and critique in the middle, and end with something positive.
3) Give suggestions for improvement. Instead of just saying “I don’t like this” say what you would have done differently. Critiques are a fantastic opportunity to learn and to teach.
When teaching a workshop and a critique session is involved (they usually are in my workshops) these are the three rules I tell students. However, in the online world, I think a few additional reminders are helpful.
4) Respect others opinions. I don’t agree with anyone 100% of the time, and you probably don’t either. It’s okay to like something that others don’t and vise versa. Photography is very subjective. You can feel differently about a photo than someone else does without either of you being wrong.
5) Be honest.
6) Be specific. Try to pin point what you like and don’t like about an image. Just saying “I like this” or “It doesn’t work for me” isn’t all that helpful. While some very general feedback may be quick and easy to offer, if your goal is to help someone learn and improve your own critiquing skills, it is worth the time and effort to go a little more in depth than a single generic sentence.
7) Don’t give a critique if it isn’t asked for. Some venues are specifically for critiquing photos, such as photo contests, online photo critiquing forums*, and some art galleries. However, many people just want to share their images and if someone is posting a photo to their own social media or website, it’s generally not appropriate to criticize their work. Offering a critique when it isn’t asked for is akin to bullying; just don’t do it. In situations where a critique is not asked for, the old adage applies: if you don’t have anything nice to say, don’t say anything at all. *Note: Most online photo sharing websites, forums, and Facebook groups have clearly stated rules. It is really important to familiarize yourselves with the guidelines of any groups you belong to and adhere to them.
Here is a sample image with examples of a not-so-good critique and a much better one:

Bad critique: This shot is kind of boring, but the fish looks cool!
Why it’s bad: The assessment is negative, and the commenter didn’t provide any specific details, so the photographer doesn’t know how to improve.
Better critique: While this is a really pretty fish, I don’t find the image very interesting and the background is a bit distracting. I find that the green blob in the lower right distracts from the otherwise uniform blue and gold color scheme, and the fish eyeball in the top left corner is a bit awkward. Maybe a slight crop would help? You positioned the fish in the frame nicely though, and the detail is good. This would be a good shot to illustrate this type of fish for a guide book or aquarium display, because you can clearly see the markings and outline of the fish.
Why it’s better: Even though this comment contains some critical elements, the commenter leads off with a positive note before diving into what they don’t like about the image. In addition to specifically pointing out areas that could be improved, the commenter also focuses on areas where the photographer did well and ends with a compliment.
While I will argue that social media is not good for a lot of things, using the online photography community and social media platforms to share and get feedback on photographs can be a fantastic way to improve your photography skills. By developing solid critiquing skills and providing respectful, thoughtful feedback to others, you are more likely to receive helpful critiques and advise regarding your own work, plus people will like you! Critiquing is an art, one that takes skill, time, and practice to perfect, but following my tips above should help. Good luck!