There are millions of ways to achieve this, but none better than to have a professional handle it. They scan your photos so you can keep the family album in tact. The photos you send are returned unharmed. If you have digital photos from your camera or cell phone, they can probably be used in the collage as well, depending on their resolution, of course. The larger the MP (megapixel) the better. 4-5MP work fine. Anything higher will only help to increase the collages' sharpness.
The hardest part of the entire process is choosing the photos to use. Of the hundreds of photos you have, narrowing them down to 40 or so is extremely difficult. I know this because when I had my family's photo collage created, I spent HOURS trying to find the best photos and make sure everyone had an equal amount of “exposure.”
A very common size is the 24"x18" using approx. 40 photos. They are arranged in a balanced way using both color and content. Having a large, main center photo helps achieve a focal point to the collage when viewed from across the room. Black & white photos mix well with color photos and look neat next to each other in the collage. It's very cool to see your mother as a child next to you at the same age.
ProCollage (Professional Digital Photo Collages) can usually have your collage completed in less than a week. The proof of your collage is sent to you via email so you can see it before it goes to print. And speaking of the print... it's breathtaking! Seeing it for the first time makes your jaw drop. But, best of all is having it hung in your house, passing by it virtually everyday and suddenly one day noticing a photo that you didn't see originally!
All in all, the photo collage was the best gift I ever gave my parents and I know it will be for you too. Anniversaries, Mother's Day, Father's Day, Birthdays or really any day... they will absolutely love, adore and treasure it forever.