What are the main rules of thumb about fair use on the web?
The number one piece of advice: Assume it’s protected.
I'll give you other tips below for you:
Just because its online, doesn't mean that it’s public property. So many people have this false sense of entitlement to anything they see posted on social media "especially pictures".
If someone complains, just remove the content for the time being. No, you don’t have to sell your soul to every troll on the Internet who demands that you remove content from your site, but you should take it down long enough to research to make sure they don’t have a legitimate legal complaint.
Remember that always, always, always ask first. If you see awesome photographs you want to post on your blog and website or other social network, just ask first. Sometimes people are totally fine with exposure as long as they are properly credited.
Copyright is a murky area and you don’t want to get caught up in an unnecessary legal battle over a picture or two. So save yourself some trouble and just take some of the precautions.
If you’d like some more help with understanding copyright laws, we can connect you with a skilled copyright attorney in Vietnam that can answer your questions and potentially help you avoid a costly mistake.