How to Open .ITHMB Files

ITHMB (short for iThumbnail — Apple's thumbnail image format) is a binary container format used by Apple's iOS and macOS to store thumbnail caches. You'll find these files scattered inside PhotoData folders on old iPods, iPhones, and Macs when recovering data, migrating devices, or digging through backups. They don't open with a regular image viewer. This guide shows you how to decode them.

What Is an ITHMB File?

Apple created the ITHMB format to batch-store small thumbnail images in a single file. Apps like Photos, Preview, and Finder use it to serve up thumbnail previews without loading the full-resolution originals. The format packs multiple JPEG images together with a binary index, which is why double-clicking an .ithmb file does nothing useful on its own.

ITHMB files are most commonly encountered when extracting data from older Apple devices (iPhone 3G through iPhone 5-era, early iPod Touch models, and Macs running macOS 10.4 through 10.14). If you've ever copied a “PhotoData” folder from an iPod or iPhone backup, you've probably seen them. The closely related .ipm format works the same way for iPod Photo caches.

How to Use the Free Online Decoder

The fastest way to open ithmb online is the free ITHMB to JPEG converter built by the Ithmb-Codec project. It runs entirely in your browser and needs no installation. Here's how:

1. Go to the decoder. Open ithmb-codec.dev/ithmb-decoder in any modern browser (Chrome, Firefox, Safari, Edge).
2. Drag and drop your .ithmb files. You can drag one file or many at once. The decoder also accepts .ipm files.
3. View and download as JPEG. Each thumbnail in the container is extracted and displayed. Download individual images or grab them all at once as a ZIP archive.

That's it. No account, no upload button, no waiting. The decoder is the most straightforward online ITHMB viewer available.

Why Use This Decoder?

• Private. No data leaves your computer. The decoder runs via WebAssembly with zero server uploads. Your thumbnail files never touch a network.
• Fast. The WebAssembly core processes files locally at near-native speed. Even large .ithmb containers decode in seconds.
• Free. No paywalls, no limits on file size or batch count. It always works at zero cost.
• Open source. Every line of code is public on GitHub. No hidden tracking, no analytics, no data collection.
• Batch support. Drop multiple .ithmb files at once and download them all as a single ZIP.

If you're looking to convert ithmb to jpg in bulk or just need to extract iPod photos from an old backup, this is the simplest tool for the job.

About the ITHMB Codec Project

Ithmb-Codec is an open-source reverse-engineering effort to document and decode Apple's proprietary thumbnail container formats. The project maintains the reference decoder library (written in Rust, compiled to WebAssembly), the browser-based decoder linked above, and format documentation for researchers and digital archivists.

Bug reports and format samples are always welcome — open an issue on GitHub and we'll investigate. The project is open for everyone.

Frequently Asked Questions