SketchersGrid provides you with a photo grid overlay from which you can sketch or paint. It also allows you to quickly compare a photo of your current work against composition rules such as the rule of thirds.
Different grid colors may chosen to find better contrasting colors for your image, and each image can be saved along with the color choice and grid location settings.
The grid can be resized and moved around the image, and then tapped to focus the view on just the grid area without deleting the original image.
SketchersGrid also offers an action app extension called View Composition allowing you to display an image from another application (such as Photos, Procreate, etc) with the default rule-of-thirds hairline overlay to verify your composition.