Automated web testing techniques infer models from a given web app, which are used for test generation. From a testing viewpoint, such an inferred model should contain the minimal set of states that are distinct, yet, adequately cover the app’s main functionalities. In practice, models inferred automatically are affected by near-duplicates, i.e., replicas of the same functional webpage differing only by small insignificant changes. We present the first study of near-duplicate detection algorithms used in within app model inference. We first characterize functional near-duplicates by classifying a random sample of state-pairs, from 493k pairs of webpages obtained from over 6,000 websites, into three categories, namely clone, near-duplicate, and distinct. We systematically compute thresholds that define the boundaries of these categories for each detection technique. We then use these thresholds to evaluate 10 near-duplicate detection techniques from three different domains, namely, information retrieval, web testing, and computer vision on nine open-source web apps. Our study highlights the challenges posed in automatically inferring a model for any given web app. Our findings show that even with the best thresholds, no algorithm is able to accurately detect all functional near-duplicates within apps, without sacrificing coverage.