Read the full post at Bellingcat.
When conducting open source investigations, an ever-present issue is how to archive away the materials you are researching. For example, a social media post may be deleted by a user after you publish an investigation, or a video on YouTube showing sensitive information (such as a war crime in Syria) may be deleted due to censorship policies set by YouTube.
There are two main reasons to archive all of the digital evidence that you use an investigation: to preserve it in case it is removed from its original source, and to prove to your audience that the material (if it has been removed) really existed as you present it. Screenshots can be easily forged, so it is vital that you find a way to retain the materials in a way that shows that you did not have the opportunity to modify the content.