[usernamesarelame]

Well, not really combining them.
It's more lie you have one photo, then another, then another and it makes almost a video kind of thing.
o-o

Like this;

[princessdontmess]

Use gif ninja,
gifninja.com - create a gif from existing files

[carmitee]

IDK

[sweetvicky]

Photoshop ...

[sage-of-lead]

You need to create a .gif file, many programs exist which allow you to do so. I suggest researching with your search engines and looking more into creating .gif images.