Overview

The initial screen when the phone is locked as well as the home screen has a background that can easily be changed from the settings menu. To import pictures from a mac, create a folder in iPhoto called "iPhone Wallpapers" or something similar. Copy the backgrounds you would like into that folder. Then in iTunes tell it to sync that folder with your iPhone. It will then create an album on the iPhone you can use to set the wallpapers.

It is also worth noting you don't have to create a background before using it since you can crop and zoom in on any photo you have in the iPhone. The problem comes up when you are zooming in on a photo. iTunes "optimizes" the photos for the iPhone, meaning it reduces the quality. So when you zoom in on an image things can start to look grainy. If you create an image initially at the correct resolution then you will have as good a quality picture as possible.

Keep in mind when creating your backgrounds that the top and bottom portions of the screen will have information like the time or the slider. I've seen several backgrounds that take advantage of the full screen. Although they look good on the computer once you import them into the iPhone you'll see someone's head chopped off or some other issue. Just try to imagine a slightly elongated and slightly lowered from center box and make sure the main subject of the image is in there. You can always just import the full image and resize it. Once it looks how you like you can then duplicate the settings in your photo editor.

If you are looking for free photo editors, I would recommend Paint.Net for windows or Seashore for os x.

Backgrounds

Here are backgrounds I have made. All the pictures on here are created by me and are released under the same creative commons license this whole site is licensed (see bottom of page for link to details). It would be nice if you used one in some open source project that you let me know but isn't required.

Click on the image to view the full version to save. If you have javascript enabled it will "zoom in" to the full sized image. You can then right click and save the image as usual.

iPhone 5 or higher

These have been resized to the 1136x640 resolution of the 16:9 "retina" display found on the iPhone 5 and above

Mahuri by Niabot
"Mahuri" (even higher res version of below) by Niabot (source)
 

iPhone 4 series

These have been resized to the 960x640 resolution of the "retina" display found on the iPhone 4 and above

Mahuri by Niabot
"Mahuri" (high res version of below) by Niabot (source)
 

iPhone 3Gs or older

These match the 320x480 screen of the 3Gs or older. They will work with newer phones but won't be as sharp

Mahuri by Niabot
"Mahuri" by Niabot (source)
small section of a large galaxy
Small section of a large galaxy
from lucky star
From Lucky Star
unknown anime
Source unknown
tifay from finaly fantazy VII advent children
"Tifa" from Final Fantasy VII: Advent Children
Kate Beckinsale as Selene in Underworld
Kate Beckinsale as "Selene" in Underworld: Evolution
smarties
Smarties. Source: PublicDomainPictures.net
do not ride
 
fractal
Fractal I made a while ago
fractal 2
Fractal made by someone else
welcome to imac
Was from a "welcome to imac" background, think series was called iCandy or something
unknown anime pet
Source unknown
Izumo
From Izumo
pia carrot
From Pia Carrot
green orb
From some random background I have

Additional Resources

Here are some external sites that have a lot of backgrounds