When I put the wallpaper in
/dcim/Camera and go to change the wallpaper and choose
Media gallery and I select the wallpaper I want, it asks me to choose only a small region of the image. What do I need to do to use the entire image?
The above answer is vague. Here's a more complete answer.
Go through the wallpaper settings and open the image you want to use for wallpaper. You will be prompted to crop it.
Drag the cropping reticule to the bottom right corner.
Drag the left edge of the cropping reticule all the way to the left edge of the screen. The reticule should grow to encompass the whole image.
Tap the "Crop" button at the top right. It will "crop" the image to the size that it already is, and set it as your wallpaper.
All this because the developers who wrote the wallpaper cropping app couldn't be bothered to check whether the selected image is already the correct size for the device. All they had to do was say "This image is already the right size. Would you like to crop it anyway?", and give us buttons labeled "Crop It" and "Just Use It". Instead, we're stuck with this thoroughly non-intuitive mess.
Well done, Android devs. slow clap
In case anyone is curious, the wallpaper shown in the screenshots above comes along with McKinley Tabor's excellent Asus Transformer Prime Wallpaper Template.