  Embedding invisible hyperlinks or hidden codes in images to replace QR codes
has become a hot topic recently. This technology requires first localizing the
embedded region in the captured photos before decoding. Existing methods that
train models to find the invisible embedded region struggle to obtain accurate
localization results, leading to degraded decoding accuracy. This limitation is
primarily because the CNN network is sensitive to low-frequency signals, while
the embedded signal is typically in the high-frequency form. Based on this,
this paper proposes a Dual-Branch Dual-Head (DBDH) neural network tailored for
the precise localization of invisible embedded regions. Specifically, DBDH uses
a low-level texture branch containing 62 high-pass filters to capture the
high-frequency signals induced by embedding. A high-level context branch is
used to extract discriminative features between the embedded and normal
regions. DBDH employs a detection head to directly detect the four vertices of
the embedding region. In addition, we introduce an extra segmentation head to
segment the mask of the embedding region during training. The segmentation head
provides pixel-level supervision for model learning, facilitating better
learning of the embedded signals. Based on two state-of-the-art invisible
offline-to-online messaging methods, we construct two datasets and augmentation
strategies for training and testing localization models. Extensive experiments
demonstrate the superior performance of the proposed DBDH over existing
methods.
