If you have an image-editing tool that can dramatize an image right away, this is the vignette. This hides the corners of a photo, highlighting the center of the image without you having to bother. Previously, you had to search on your iPhone outside the photo app to achieve such a result. On iOS 13, however, a vignette is immediately available.
To add a vignette to an image, tap Edit. in the upper right corner while the picture is displayed. Then scroll to the right on the effect carousel. Here you will find "Vignette" with the default setting "0". Swipe the slider to the right to increase the vignette effect to 100, and swipe left to reverse the vignette (the edges turn white instead of black) and decrease to -1
If you're satisfied with your vignette effect, you can look at the bottom right corner of the screen tap on "Done". If you want to deactivate the effect again, just tap on "Cancel".