If you have 2 photos, one "then" and one "now", that you'd like to combine into one composite photo (such as I did in a previous blog post), you'll need to use photo editing software that, 1) allows you to work in layers, 2) allows you to adjust the transparency of a photo, and 3) allows you to transform an image (resize, skew, distort, perspective, etc.). There are a number of software programs out there that will accomplish these tasks. Here are few for your consideration...
Photoshop The current version is CS4 but a new version, CS5, will be available May 25th. This is the granddaddy of photo editing software. It does all three things you need to create composite photos and SOOO much more. It's overkill, really, unless photo editing is your business. You can preorder CS5 for $699 or if you just can't wait you can order it now for $668.02 on Amazon.com. If you buy this, and you have no previous experience with photo editing software, be prepared to be overwhelmed. You'll need a class or two (or three!) to help you navigate your way around all the tools available.
Photoshop Elements The current version is 8.0. It's the little brother to the full version of Photoshop. It's currently selling for $69. This is a terrific "lite" version of Photoshop and it too does all three things you need to create composite photos and much more. It's a great piece of software for digital scrapbooking too, if you're so inclined. It's intended for the hobbiest and it doesn't have all the advanced features of the full version of Photoshop. It's not exactly intuitive to first time users but there are many, many, free tutorials available on the web to help you learn how to use it. I use this software daily and I highly recommend it.
Corel PaintShop Pro The current version is 3X. It's made by the same folks who created CorelDraw and like Photoshop Elements it too is currently selling for $69. This program is more similar to the full version of Photoshop than to Photoshop Elements. Actually, I take that back. It's the best of both worlds! It has an advanced feature set similar to Photoshop and can work with RAW photos but it also has the tools and workspace to make digital scrapbooking fun and easy. It will have a steep learning curve though in order to use all its tools. Needless to say, it has the three functions you need to create composite pictures and lots more. I used this software for years and preferred it Photoshop. I find it much more intuitive to use. However, be aware that the default settings create a propriatary file format that is not as commonly found around the net (translation: you won't find as many users, message boards, tutorials, presets, etc. for PaintShop Pro). Still, I highly recommend it.
GIMP The current version is 2.6. It an open source program (free) that does all three functions you'll need to create a composite photo and much more. I have never used GIMP and honestly, I don't know a lot about it. I went to the web site and looked into downloading the program and immediately got overwhelmed with Geek-Speak. I think this program is for those with a techie bent.
Paint.NET The current version is 3.5.5. This too is an open source program (free) that is a bit easier to download and learn than GIMP. It has two of the functions you need for creating a composite photo (it allows you to work in layers and adjust the transparency) but I couldn't find the third function (transformation) when I looked through it. If someone knows where to find this function in Paint.NET please leave a note in the comments section below this post.
There may be other software programs available that have the three functions you need to create a composite photo. If you don't find one to your liking in my list, try a Google search. (Picasa and Picnik do not have the functions you need to create composite photos.)
Next up, the nuts and bolts of creating a composite picture...
Creating a Composite Photo, Part 3
Creating a Composite Photo, Part 1