You can merge two photos online by using imgonline.com.ua.
If you have more than 2 photos that you need two combine together this website will help you.
You can specify 2 images of different file formats such as bmp, gif, jpeg, png, and tiff.
Go to: IMGonline.com.ua
You can merge two photos either horizontally (second picture on the right) or vertically (second picture below). The automatic adjustment with various option helps you merge 2 photos in the best possible ways.
For more such websites try: Merge two photos online for free.
You can also rotate either of the pictures. There is an option to trim 1st or the 2nd image, mirror reflection, size optimization.
And finally, you can set output format of the image, JPG for standard or progressive with quality or png with transparency.