1. Create a new file choosing A4 in the Preset dropdown. If you cannot see the rulers displayed on the top and left side toggle them on [apple+R] [ctrl+R]. Click and drag a guide from the left ruler, when you near the centre of the page, the guide should 'snap' into place automatically (if it does not snap, check that View>Snap/Snap To>Guides are ticked).

2. Open a photo file and drag it onto your A4 file. (You could use a photo which has already had a border added via the custom action we created previously). Allow the photo to snap to the guide.

3. Now add a drop shadow, (again you could use the custom action we set up before).

4. With the photo layer selected apply a Transform with Edit>Transform>Rotate and offset the photo horizontally. You should have something resembling the images on the right.

5. Repeat steps 2, 3 and 4 to add a few more images to your A4 layout. The finished result as shown here will be an interesting collage alternative to an edge-to-edge-boxes layout.