A major challenge for ATR evaluation is developing an accurate image truth that can be compared to an ATR algorithm's decisions to assess performance. We have developed a semi-automated video truthing application, called START, that greatly improves the productivity of an operator truthing video sequences. The user, after previewing the video selects a set of salient frames (called "keyframes"), each corresponding to significant events in the video. These keyframes are then manually truthed. We provide a spectrum of truthing tools that generates truth for additional frames from the keyframes. These tools include: fully-automatic feature tracking, interpolation, and completely manual methods. The application uses a set of diagnostic measures to manage the user's attention, flagging portions in the video for which the computed truth needs review. This changes the role of the operator from raw data entry, to that of expert appraiser supervising the quality of the image truth. We have implemented a number of graphical displays summarizing the video truthing at various timescales. Additionally, we can view the track information, showing only the lifespan information of the entities involved. A combination of these displays allows the user to manage their resources more effectively. Two studies have been conducted that have shown the utility of START: one focusing on the accuracy of the automated truthing process, and the other focusing on usability issues of the application by a set of expert users.