We usually recommend that the images should be at least the same size as the format of the videos in order for them to be of good quality.
The recommended size of pictures:
1:1 = 1080x1080 px
4:5 = 1080×1350 px
16:9 = 1920x1080 px
9:16 = 1080x1920 px
The maximum size for a single file in Storykit is 1GB (or 10000px x 10000px) but we recommend you upload files in approximately 4K resolution.