How to merge pictures?

How about Microsoft paint. Any basic tool like this should enable you to save the completed merged photo as a new image ready to up load. Not sure what you would use if you're using Mac software but I bet the have a drawing tool that's similar.

I recommend IrfanView. It's free and gives you a bit more functionality than Paint.

You can get it here: http://www.irfanview.com/

It's not the prettiest application, but it allows you to take screen shots, edit pics, resize pics, combine pics (by copy/paste) into a single picture file as well as add text/draw lines on your pics.

There's tons of these kind of applications out there, but not very many free ones that let you do as much as IrfanView.

If you have an iPhone, there is a very easy (and free!) app called PicStitch. (It may be available on Android as well.) This works well if your progress pics are on your phone. I take my monthly shots on the phone, and they then I open PicStitch. There are several options of how many pictures and the layout. Then you can e-mail it, save it to your camera roll, or post it to Facebook.

*My profile picture was made this way.

You probably already have paint on your computer, and it's pretty easy to use.
Assuming both images are the same size and just need to be placed beside each other all you need to do is open two copies of paint, one image in each that you want to use (one for your before, one for the after), and then copy your second image itno the first. How to:

On the first image look along the middle of the right edge for a little box Your mouse should change to a <-> looking pointer when you hover over it. Click and drag far to the right, a bit larger then the other image you have open. Go to your second image, use ctrl+a to select the image, then ctrl+c to copy. Go back to your first image and click ctrl+V to paste. Before you click anywhere else, click your pasted image and move it to the right, into the blank space you created by moving the side to the right. Position, then select something (anyhting) outside of the copied image to release the selection you were moving. Hover over the middle of the right edge again to move it in tot he edge of your copied image so you don't have a white line along one side. Voila, you are done.

If anyone needs help with image editing feel free to send me questions.

There is a program called Gimp which is available at http://www.gimp.org . It is a completely free program which is written by the public which submit their code suggestions and programmers check the code - it is as near to photoshop as you will get without paying. Some people even say it is better than photoshop. The basic download has many features, then there are other things on top of that you can download from the site. When you've edited photos in that the way you want (I took out my backgrounds and made them plain for my side to sides) you then export your photos back to JPEG format so you can display them if you want on the web.

Yep, Gimp is also an excellent tool for this - and it's free!