SAN JOSE: A Samsung Electronics Co Ltd expert witness testified on Tuesday that Apple Inc's iPhone and iPad violate three of Samsung's patents, as the South Korean electronics company went on offense in the third week of a high stakes trial.

Dr. Woodward Yang, an electrical engineering professor at Harvard, said Apple's products use Samsung-patented features for mobile devices, including the process for seamlessly emailing photos. He was one of Samsung's first witnesses after a parade of Apple experts said Samsung phones and tablets violated Apple's patents.

Apple and Samsung are going toe-to-toe in a patents dispute mirroring a struggle for industry supremacy between two rivals that control more than half of worldwide smartphone sales.

The US company accuses Samsung of copying the design and some features of its iPad and iPhone, and is asking for a sales ban in addition to monetary damages. The Korean company, which is trying to expand in the United States, says Apple infringed several patents, including some for its key wireless technology.

Apple concluded presenting evidence regarding its own patents this week, and Samsung started calling witnesses. On Tuesday, Yang said Samsung's patents were filed before the introduction of the iPhone in 2007.

Yang focused on patents that cover smartphone features, not wireless technology. One of those patents covers technology for easily finding photos in an album.

“The idea here was, let's have a bookmark,” Yang said.

Additionally, in an attempt to invalidate some of Apple's patents in the case, Samsung presented evidence this week to show that Apple's patents cover technological advances -- like multitouch -- that had already been developed before Apple claims to have invented it.

The case in US District Court, Northern District of California, is Apple Inc v. Samsung Electronics Co Ltd et al, No. 11-1846.