The internet can seem at times a terrible, negative place, but it can also be a tremendous resource for collaboration and sharing. People the world over are willing to take the time and effort to create fantastic works of art, photography and video, and many are willing to share them with everyone with no desire for compensation. Others ask simply that users attribute the material they use and follow a licensing agreement. While that may not seem a particularly onerous requirement for the free use of others' works, many companies and individuals still manage to get themselves in trouble by not reading those agreements.
An Italian festival found themselves having to apologize after incorrectly using a photographer's work in their promotional materials. The Festival delle Resistenze 2016 created promotional materials that used a photo of one of their speakers, Federico Rampini, pulled from Wikimedia Commons. That photo of Rampini was taken and uploaded by Niccolò Caranti and subject to the Creative Commons BY-SA 4.0 license, which permits free use so long as attribution is given, and changes made are noted, and any redistribution is under the same license.
Unfortunately, the festival organizers failed to give proper attribution to Caranti for the photo, which he saw on a poster for the event. Caranti decided to take legal action against the organizers, issuing a cease and desist letter through his attorney. The agency that handled bookings for Rampini stepped in and admitted fault on their part, stating that they inadvertently sent the photo they had grabbed from the internet rather than one from their own archives, according to a blog post from Caranti's attorney. A settlement was reached between Caranti and the organizers that paid Caranti's legal costs as well as compensation, as well as statements of apology from the festival and the booking organization and correct attribution on the photograph.
Simply because a photograph online may not have a licensing fee attached to it doesn't mean that there aren't agreements or conditions attached. Before you use anything that you find online and haven't created yourself, be sure to read any and all licensing agreements related to that work to make sure that you are complying. Ignorance isn't a defense should you end up in a legal battle.