I need some photos that an app use, can i get them? I'm talking about zombiebooth app. I need those photos of damaged body parts for an after effects project. I guess they are saved as .png and i want those files, how can i get them?
You can extract the apk file (which is just a jar/zip file) and find the folder where the app stores the images, it is usually in the res folder, but it may be different place. If the app use APK expansion, then the image may also be stored in the expansion file. 

Note that you may be violating the copyright of the developer by using these images, it's better if you contact the developer and request permission to use these images.