The legality of screen scraping is far from simple to address. Laws, where they exist, differ by jurisdiction, and court rulings seem ambiguous at best. This is not surprising as most cases against scrapers are brought using laws that were intended for other types of abuse. It is generally a good idea to obtain a legal postion from counsel with expertise in the jurisdiction where your site operates.
In spirit, most courts have agreed that scraping is unlawful. That doesn’t mean by any means that decisions have generally gone against scrapers. A good proportion of the limited cases that have been brought would be eligible for the top ten legal blooper’s reel. Several positive decisions against scrapers have been overturned on appeal as a result of bad legal maneuvers.
One drawback in a legal battle against scrapers is not always that easy to identify the actual scraper as they use various anonymizing techniques. Identifying scraping activity, and stopping it is a more realistic goal. It is far less expensive, faster, and has proven to be more effective. In cases where a scraper is identified, they may or may not be located in a part of the world where legal action will have any affect. Fighting to establish the jurisdiction for a trial can add years of delay to a case, and increase the cost.
In many cases the sheer numbers of scrapers involved can make legal action impractical. It is an easier task if there are only a few scrapers abusing your data, and most cases are brought against a main offender.
How well a site “tried” to stop scraping has also been a factor. Just blocking an IP address, properly configured robot.txt files, and/or using a CAPTCHA has come up short in some courts as not doing enough to stop scraping. In the case of the scraping of tickets, ticket retailers have been instructed that they need to have a clear anti gaming strategy to stop scrapers. Needless to say, it is not very clear how much is enough.
Certain types of data get more protection from some legal systems. Photos get special treatment where descriptions of the same photos get very little.
One positive thought is that indemnification doesn’t hold for a felony. So if you are being scraped by one of the larger scraping service providers, there may be some one involved with something to lose.