  In the multimedia era, image is an effective medium in search advertising.
Dynamic Image Advertising (DIA), a system that matches queries with ad images
and generates multimodal ads, is introduced to improve user experience and ad
revenue. The core of DIA is a query-image matching module performing ad image
retrieval and relevance modeling. Current query-image matching suffers from
limited and inconsistent data, and insufficient cross-modal interaction. Also,
the separate optimization of retrieval and relevance models affects overall
performance. To address this issue, we propose a vision-language framework
consisting of two parts. First, we train a base model on large-scale image-text
pairs to learn general multimodal representation. Then, we fine-tune the base
model on advertising business data, unifying relevance modeling and retrieval
through multi-objective learning. Our framework has been implemented in Baidu
search advertising system "Phoneix Nest". Online evaluation shows that it
improves cost per mille (CPM) and click-through rate (CTR) by 1.04% and 1.865%.
