There are several scrapbook technique and rules to keep in mind when cropping your photos.
1. Never crop out anything that identifies the era. That car or toy in the background will make a photo more interesting in years to come.
2. Do not crop old or important photos.
3. Cropping is irreversible. Have copies done and crop those instead.
4. Scan your photo onto your computer, save it and open it in your photo program. Crop your photo there and make any corrections to that photo as well. Then, you can enlarge or shrink to preferred size and print.
5. Never crop Polaroid's as the chemicals will leech out and may cause skin and eye irritation.
One scrapbook matting technique is to crop a copy fo the photo or use a frame around the Polaroid on your page.