When you add a still image, you can assign a specific duration to it. The duration specifies how much time the image occupies in the Quick view/Expert view timeline. You can set a default duration for all still images that you add, and you can change their duration in the Quick view/Expert view timeline.
The frame rate of your project determines the amount of time that a certain number of frames occupies. If you specify 30 frames for a 29.97 frame‑per‑second (fps) NTSC project, each still image has a duration of about one second. For PAL, if you specify 25 frames for a 25-fps project, each still image in the Quick view/Expert view timeline has a duration of one second.