IPA File Format

An IPA archive is the de facto way to package applications for iOS. The extension has no official definition, but is commonly called iPhone Application by the iOS community. The file is just a renamed ZIP archive. Although any computer with a ZIP archive reader can extract an IPA, PNG images (e.g. the app's icon files) are typically in a proprietary variant of the PNG format instead of the standardized PNG format, and the application binary is encrypted (DRM) which prevents examination of the binary.

Contents
As an IPA file is just a renamed ZIP archive, its structure is available from PKWARE.
 * (various application files)
 * (various application files)
 * (various application files)
 * (various application files)
 * (various application files)

iTunesArtwork
As per Technical Q&A QA1686, the  file should be a PNG image. However, Apple, among many other developers, contradict this by using JPEGs instead.

Examination of nearly any  file with a hex editor can be used to confirm this. If the file's first two bytes are  (hex), the file is a JPEG. If the first 8 bytes are  (hex), the file is a PNG.

Usage
Apple uses the IPA format for packaging iOS aplications. iTunes can be used to install their contents on a device, provided the included files are signed. Developers can use the IPA format for Ad Hoc Distribution of their apps.

Creation
IPA files are typically created through Xcode, but may be created manually:
 * 1) Build application
 * 2) Locate the   folder
 * 3) Create a folder named
 * 4) Place your   folder in it
 * 5) Create a 512x512 JPEG version of your icon (see above section)
 * 6) Save it as   (no extension)
 * 7) Create your   and save it
 * 8) "ZIP" the contents