Off the top of my head (Which may not be a great example but the first one that sprung to mind) Field v. Google.
> The Field court expanded the earlier doctrine to hold that implied license arises "where the copyright holder knows of the use and encourages it." Applying this two-pronged knowledge and encouragement test to the Field facts, the court found that the website owner was aware of the robots exclusion protocol mechanisms for communicating with the Googlebot, and that by not using them, he essentially encouraged the Googlebot to index his content.
I think that's a stretch. Field did a lot more than just fail to defend his copyright:
> Field created a robots.txt file for his site and set the permissions within this file to allow all robots to visit and index all of the pages on the site. [...] Field created the robots.txt file because he wanted search engines to visit his site and include the site within their search results.
and (regarding meta-tags):
> Field concedes he was aware of these industry standard mechanisms, and knew that the presence of a “no archive” meta-tag on the pages of his Web site would have informed Google not to display “Cached” links to his pages. Despite this knowledge, Field chose not to include the no-archive meta-tag on the pages of his site. He did so, knowing that Google would interpret the absence of the meta-tag as permission to allow access to the pages via “Cached” links. Thus, with knowledge of how Google would use the copyrighted works he placed on those pages, and with knowledge that he could prevent such use, Field instead made a conscious decision to permit it. His conduct is reasonably interpreted as the grant of a license to Google for that use.
Field was trying to get his site indexed and cached (so that he could sue Google), and Google indexed and cached it. The court ruled that Field's actions were active encouragement and implied the grant of a license to do the thing he wanted Google to do.
Came back and realized I should have worded that second sentence better.
Field didn't fail to defend his copyright. He put the files up in January, filed copyrights with the Copyright office, waited for them to be indexed and cached, and sued Google in April. He protected his copyright about as vigorously as you can with the available legal tools.
The question of implied license in this case is whether putting something on the internet without taking steps to stop search engines from indexing+caching it constitutes an implied license. The court ruled it did, but it relied in part on Field taking specific actions to allow it (such as the robots.txt file), so it's not entirely clear that in a different case they would rule the same way. If someone put up a site with just a plain text file without HTML tags and no robots.txt file maybe the court would rule that there was not an implied license there, I don't know. They also took into consideration that there are well-known industry standard ways of preventing Google and others from indexing and caching your site, so maybe they would consider that alone sufficient to rule that there's an implied license if you don't follow the industry standards.
In any case, Field v. Google has little-to-nothing to do with failing to defend a copyright.
Off the top of my head (Which may not be a great example but the first one that sprung to mind) Field v. Google.
> The Field court expanded the earlier doctrine to hold that implied license arises "where the copyright holder knows of the use and encourages it." Applying this two-pronged knowledge and encouragement test to the Field facts, the court found that the website owner was aware of the robots exclusion protocol mechanisms for communicating with the Googlebot, and that by not using them, he essentially encouraged the Googlebot to index his content.