1- Open Affinity Designer
2-Open a photo.
3- Create a new layer in the layer palette.
4- Create a vector shape. It can be any colour.
5- Resize the shape and place where you would like it to be on your image.
6- In the layers panel,drag the object layer over onto the background layer. The image will now appear in the shape.
7- Select the effects options in the layers panel.
8- You can add effects like blur and change the amount of blur.
9- In the layers palette, by selecting only the mask and not the background, you will be able to move the shape around to ensure the correct part of the background is showing.
10- If you select both the background and the mask both the image and the shape will move together.