功能简介 About
「留证鸭」是专为租客打造的押金保卫战工具：拍照自动加盖时间戳水印（位置可选）、水电气表读数记录与差值计算、短视频留证、物品清单三态登记、入住/退租对比拍摄、PDF 证据包导出、催告函生成器、双方签名交接页、照片 SHA-256 防篡改指纹、证据时间线提醒。从入住第一天到退租交接，每一步证据都帮你安排明白。纯本地离线运行，无注册、零广告。
"RentCheck" is a deposit-protection toolkit for renters: timestamped watermarked photos (optional location), utility meter readings with automatic difference calculation, video evidence, three-state item checklists, move-in/move-out comparison shots, PDF evidence packs, demand-letter generator, dual-signature handover pages, SHA-256 photo fingerprints, and evidence timeline reminders. Fully offline, no account, no ads.
App Store：在 App Store 搜索「留证鸭」即可下载。/ Search "留证鸭" on the App Store.
常见问题 FAQ
1. 照片水印是怎么加上的？ / How are watermarks added?
时间戳（以及可选的位置）水印在拍摄时直接烧入照片像素，无法被无痕篡改，配合 SHA-256 指纹可自证完整性。The timestamp (and optional location) is burned into the photo pixels at capture time; combined with the SHA-256 fingerprint, each photo's integrity is self-verifiable.
2. 催告函有法律效力吗？ / Is the demand letter legally valid?
催告函基于《民法典》相关条款（577、585、733 条）自动生成，供协商沟通使用，仅供参考，不构成法律意见。重大纠纷请咨询执业律师或向住建部门、法院求助。The demand letter is generated from Civil Code references for negotiation purposes only and is not legal advice. For serious disputes, consult a licensed lawyer or the relevant authority.
3. 数据会丢失吗？换手机怎么办？ / Will I lose my data?
所有数据存在本机。换机前使用「备份指南」导出备份文件，新设备导入即可恢复。退租前建议同时把 PDF 证据包另存一份。Export a backup before switching devices; we also recommend saving a copy of your PDF evidence pack separately.
4. Pro 内购包含什么？是订阅吗？ / What does Pro include?
Pro 为一次性买断（非订阅、无后续费用）：PDF 证据包、同机位对比拍摄、催告函生成器、双方签名交接页、短视频留证、照片防篡改哈希。免费版可完整使用留证核心功能。换设备或重装后可用「恢复购买」找回。Pro is a one-time purchase (not a subscription) unlocking PDF packs, comparison shooting, the demand-letter generator, dual signatures, video evidence, and anti-tampering hashes. Use "Restore Purchases" after reinstalling.
5. 需要联网或注册吗？ / Does it need internet or login?
不需要。核心功能完全离线，无账号体系，不收集任何个人数据。位置权限仅在你使用定位水印时按需申请。No internet and no login required; location permission is requested only for the location watermark feature.