Instead of a .mov or .mp4 file, an Image Sequence is a directory of numbered image files.
Why would I want to export my recording like this?
A PNG sequence has lossless compression as well as an alpha channel. It's also provided for compatibility with some older video editors that can't import some of the other formats ScreenNinja can export in.
Because an Image Sequence isn't a single file, you are unable to set the playback rate of recordings. Instead, ScreenNinja will show the number of frames (that will be) captured.