came to a head" about fifteen years ago and experts agree that these types of claims remain complex with the outcomes hard to predict. (That may be why these cases tend to settle without court rulings.) In general, a framer is more likely to be found liable for copyright or trademark infringement if copyrighted material is modified without authorization or if customers are confused about the association between the two sites or the source of a product or service.
What about the case law? Websites that frame the content of other sites were initially perceived as stealing the other site’s content. One court found framing to be a copyright infringement because the process resulted in an unauthorized modification of the linked site. (Futuredontics Inc. v. Applied Anagramic Inc.) In another case, The Washington Post, CNN, and several other news companies sued a website, TotalNews, which framed their news content. Under the terms of a settlement agreement, TotalNews agreed to stop framing and agreed to use text-only links. Inlining and framing are often used together when displaying thumbnails of search engine results. The Ninth Circuit has ruled that such uses are fair use. There's more on the subject in this article and here's a summary of some international rulings.