Visual graphics are widely spread in digital media and are useful in many contexts of daily life. However, access to this type of graphical information remains a challenging task for people with visual impairments (VI). In this study, we designed and evaluated an on-hand vibrotactile interface that enables users with VI to explore digital graphics presented on tablets. We first conducted a set of exploratory tests with both people with VI and blindfolded (BF) people to investigate several design factors. We then conducted a comparative experiment to verify that on-hand vibrotactile cues (indicating direction and progression) can enhance the non-visual exploration of digital graphics. The results based on 12 participants with VI and 12 BF participants confirmed the usability of the technique and revealed that the visual status of the users does not impact graphics identification and comparison tasks.