  Mobile AI-Generated Content (AIGC) has achieved great attention in unleashing
the power of generative AI and scaling the AIGC services. By employing numerous
Mobile AIGC Service Providers (MASPs), ubiquitous and low-latency AIGC services
for clients can be realized. Nonetheless, the interactions between clients and
MASPs in public mobile networks, pertaining to three key mechanisms, namely
MASP selection, payment scheme, and fee-ownership transfer, are unprotected. In
this paper, we design the above mechanisms using a systematic approach and
present the first blockchain to protect mobile AIGC, called ProSecutor.
Specifically, by roll-up and layer-2 channels, ProSecutor forms a two-layer
architecture, realizing tamper-proof data recording and atomic fee-ownership
transfer with high resource efficiency. Then, we present the
Objective-Subjective Service Assessment (OS^{2}A) framework, which effectively
evaluates the AIGC services by fusing the objective service quality with the
reputation-based subjective experience of the service outcome (i.e., AIGC
outputs). Deploying OS^{2}A on ProSecutor, firstly, the MASP selection can be
realized by sorting the reputation. Afterward, the contract theory is adopted
to optimize the payment scheme and help clients avoid moral hazards in mobile
networks. We implement the prototype of ProSecutor on BlockEmulator.Extensive
experiments demonstrate that ProSecutor achieves 12.5x throughput and saves
67.5\% storage resources compared with BlockEmulator. Moreover, the
effectiveness and efficiency of the proposed mechanisms are validated.
