Hugin is a free application based on the open source project called Panorama Tools. It's capable of perfectly combining a collection of photos to generate a unique global image, and all this, automatically.
Even though to obtain more control over the result it's possible to access lots of options that allow us to view the selected images, load the type of lens, crop, adjust the control points, and the exposure, etc.
You have to carry out the following steps:
1. Load the images and select the type of lens.
2. Click "Align" to automatically adjust the control points.
3. Click "Create Panoramic".
If you want to enjoy one of the best free applications to generate panoramic format photos, download Hugin.