Website accessibility is essential for inclusiveness and regulatory compliance. Although third-party advertisements (ads) are a vital revenue source for free web services, they introduce significant accessibility challenges. Leasing a website\'s space to ad-serving technologies like DoubleClick results in developers losing control over ad content accessibility. Even on highly accessible websites, third-party ads can undermine adherence to Web Content Accessibility Guidelines (WCAG). We conduct the first large-scale investigation of 430K website elements, including nearly 100K ad elements, to understand the accessibility of ads on websites. We seek to understand the prevalence of inaccessible ads and their overall impact on the accessibility of websites. Our findings show that 67% of websites experience increased accessibility violations due to ads, with common violations including Focus Visible and On Input. Popular ad-serving technologies like Taboola, DoubleClick, and RevContent often serve ads that fail to comply with WCAG standards. Even when ads are WCAG compliant, 27% of them have alternative text in ad images that misrepresents information, potentially deceiving users. Manual inspection of a sample of these misleading ads revealed that user-identifiable data is collected on 94% of websites through interactions, such as hovering or pressing enter. Since users with disabilities often rely on tools like screen readers that require hover events to access website content, they have no choice but to compromise their privacy in order to navigate website ads. Based on our findings, we further dissect the root cause of these violations and provide design guidelines to both website developers and ad-serving technologies to achieve WCAG-compliant ad integration.

翻译：网站可访问性对于实现包容性和满足监管要求至关重要。尽管第三方广告是免费网络服务的重要收入来源，但其引入了显著的可访问性挑战。将网站空间租赁给DoubleClick等广告服务技术会导致开发者失去对广告内容可访问性的控制。即使在高度可访问的网站上，第三方广告也可能破坏对《网页内容可访问性指南》（WCAG）的遵守。我们首次对43万个网站元素（包括近10万个广告元素）进行了大规模调查，以了解网站上广告的可访问性。我们旨在探究不可访问广告的普遍性及其对网站可访问性的整体影响。我们的研究结果表明，67%的网站因广告而增加了可访问性违规，常见违规包括焦点可见性和输入响应。Taboola、DoubleClick和RevContent等流行的广告服务技术经常提供不符合WCAG标准的广告。即使广告符合WCAG标准，仍有27%的广告图像中的替代文本歪曲了信息，可能误导用户。对这些误导性广告样本的手动检查显示，94%的网站通过交互（如悬停或按下回车键）收集用户可识别数据。由于残障用户通常依赖屏幕阅读器等需要悬停事件来访问网站内容的工具，他们不得不为了浏览网站广告而牺牲隐私。基于我们的发现，我们进一步剖析了这些违规的根本原因，并为网站开发者和广告服务技术提供了实现符合WCAG标准的广告集成的设计指南。