Grid or Block Style
The most traditional form of collage, a grid-style collage, can be just a group of photos aligned in rows and columns, like this sample picture. You can vary this slightly by making one or two photos larger, by making the grid more complicated with larger and smaller photos, or by adding white space between the photos to separate them and give them their own borders.
Haphazard or Jumble Collage
A more casual style is the haphazard or jumble collage, with all or most of the photos rotated slightly so they look haphazardly arranged. This type of collage works well when the photos have a border around them, or when you add a drop shadow to each photo for a three-dimensional effect and separate the photos so the image is less visually confusing.
Feathered or Blended
Instead of straight lines or borders separating your photos, you can use a feather effect, also known as blending. Feathering is a term used by graphic arts professionals, and you might see it in your photo-editing software. It means that the edge of the photo has a gradient that goes from fully opaque to fully transparent, making the edges fuzzy and blending them together.
Frame or Border Style
Perhaps you have a poem or a quote you want to feature, or one large photo that deserves center stage in your collage. Put that in the very center, larger than the other photos, and arrange the rest of the photos around the edge to form a collage frame. The key to success with this format is that the center panel should have one consistent shape, with the edges of the collage frame all lining up to form a frame around it. If your collage frames another photo, the effect will be better if you make a border between the collage and the center image, or at least add a drop shadow.
Group Gift Collage
This variation can be a collage photo or just one large group photo. The key is to leave a wide margin around the edge and give members of the group a chance to write a brief message. The messages form a frame around the center image or images. Another way to do this is to have the group members send their messages, scan them and place their digital greetings around the edge as a frame. This will make a memorable gift for someone who is retiring or moving away.
Shape Collage
Arrange your photos so that their outer edges form a shape. A heart or a cross are good choices, or just a simple circle or oval. Seasonal choices include a Christmas tree or a four-leaf clover for St. Patrick's Day.
Artistic Effect Collage
Make a collage that is really a work of art by applying some image-editing effects on your photos. Make several copies of the same photo and colorize each with a different tint, then arrange them in a grid collage. Flip a photo of someone's face horizontally, and blend it with the background, while displaying the original at a smaller size on the opposite side of the collage. Make a collage of several black and white photos and add one color photo to highlight it. Or break a picture into several images and recombine them, with borders around each, for a unique effect.
Mosaic Collage
This is a very tricky effect to create, but it is stunning when done right. You need a lot of photos that you will combine so that if you look closely, you see the individual pictures, but if you step back, you see another image made from the combination of light and dark and various colors in the photos. This style is not for beginners, so you may want to hire a professional to create a mosaic collage for you.