Managing large personal image databases requires efficient privacy preserving indexing methods to allow for their outsourcing to possibly curious cloud servers. To construct a secure inverted index in this paper, first, visual words are extracted from stored images based on the Speeded-Up and Robust Features (SURF). Next, Order Preserving Encryption (OPE) is used to encipher the frequencies of occurrence of the extracted visual words. Another scale and rotation invariant feature, which is the local HSV histogram, is included for comparison. From the obtained results, it is apparent that SURF achieves more precise results. Aggregation of both features is considered to further improve the accuracy. The effects of the weighting scheme of the visual words and their number on the performance are investigated. Weighted term frequency inverse document frequency (tf-idf) together with the Jaccard similarity measure yield the best performance. OPE encryption is shown to have minor impact on the retrieval accuracy. To reduce encryption time, a lookup table is constructed. The inverted index reduces the search time significantly compared to a sequential search scheme as apparent from the results. A comparative study with recent related schemes demonstrates the competitiveness of the implemented system in terms of computational efficiency and accuracy.

中文翻译：

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基于SURF和顺序保存加密的图像数据库隐私保存搜索索引

管理大型个人图像数据库需要有效的隐私保护索引方法，以允许将其外包给可能好奇的云服务器。为了构建安全的倒排索引，首先，基于加速和鲁棒特征（SURF）从存储的图像中提取视觉单词。接下来，使用顺序保留加密（OPE）来加密提取的可视单词的出现频率。为了比较，还包括了另一个缩放和旋转不变特征，即局部HSV直方图。从获得的结果来看，很明显SURF获得了更精确的结果。两种特征的聚集被认为可以进一步提高准确性。研究了视觉单词的加权方案及其数量对性能的影响。加权术语频率逆文档频率（tf-idf）与Jaccard相似性度量一起产生最佳性能。事实证明，OPE加密对检索精度影响不大。为了减少加密时间，构建了一个查询表。从结果可以明显看出，与顺序搜索方案相比，倒排索引显着减少了搜索时间。与最近相关方案的比较研究证明了已实施系统在计算效率和准确性方面的竞争力。从结果可以明显看出，与顺序搜索方案相比，倒排索引显着减少了搜索时间。与最近相关方案的比较研究证明了已实施系统在计算效率和准确性方面的竞争力。从结果可以明显看出，与顺序搜索方案相比，倒排索引显着减少了搜索时间。与最近相关方案的比较研究证明了已实施系统在计算效率和准确性方面的竞争力。