Online display advertising, whereby publishers display visual-based advertisements (e.g. texts, images or videos) on their website against remuneration, represents a large source of revenues for publishers, large and small, offering valuable content to Internet users. But for online display advertising, many such publishers would not subsist, and the Internet would be impoverished. Display advertising is also critical to advertisers, in particular when they seek to raise “brand awareness” among consumers.
Because of its vital importance to advertisers and publishers, healthy competition in the advertising ecosystem is desirable. Yet, despite the spectacular growth of online display advertising, the picture is not entirely rosy. In the “programmatic” era, where ad inventory is sold through computerized decision-making processes managed by “ad tech” intermediaries, the online display advertising sector is characterized by a high degree of opacity, and publishers and advertisers …