Image Format Detector

Free Online Image Format Detector

Every image file begins with a short sequence of bytes called a "magic number" or file signature, which identifies the format regardless of what the file is named. A file called photo.jpg might actually be a PNG inside, or a download might be missing its extension entirely. LovePDFImg's Image Format Detector reads these signature bytes and tells you the file's real format, and flags whether it matches the extension and declared MIME type.

This is useful for troubleshooting upload errors, verifying files before processing them in other tools, or simply confirming what format a mystery file actually is. The tool reads only the first handful of bytes from your file using the browser's File API - nothing is uploaded, and the rest of the file is never even read.

This tool is a quick fix for a common frustration: an upload form rejecting a file because its extension doesn't match its true content, or an image editor failing to open a file that was renamed incorrectly at some point.

Key Features

• True format detection: Reads file signature bytes, independent of filename.
• Mismatch flagging: Shows if the extension doesn't match the real format.
• Multiple format support: Detects JPEG, PNG, GIF, WebP, BMP, and TIFF.
• Minimal data read: Only the first few bytes of your file are examined.
• Browser-based processing: Your file never leaves your device.
• Free and unlimited: No account, no daily cap.

Who Uses Image Format Detector?

Developers: Verify a file's true format before processing it in an application that expects a specific type.

Businesses: Troubleshoot why an upload form is rejecting a file that appears to have the correct extension.

Content managers: Confirm the actual format of downloaded or received files with unclear or missing extensions.

IT support staff: Diagnose format-related upload or compatibility issues reported by users.

Why Choose LovePDFImg's Image Format Detector?

Most file-type checking tools require command-line utilities or dedicated software. LovePDFImg's Image Format Detector works entirely in your browser using the File API, with no installation and no upload. There's no account requirement, and the tool is completely free to use.

Technical Explanation: File Signatures

File signatures (also called magic numbers) are specific byte sequences at the start of a file that identify its format - for example, PNG files always begin with the bytes 89 50 4E 47, while JPEG files begin with FF D8 FF. Because these signatures are embedded in the actual file content rather than derived from the filename, they provide a much more reliable way to identify a file's true format than trusting the extension alone, which can be changed, corrupted, or simply wrong.

How to Detect an Image's Real Format

1. 1Upload your fileDrag and drop any file, or click to browse - image or otherwise.
2. 2View the detected formatThe tool reads the file's signature bytes and shows the actual format.
3. 3Compare with the extension and MIME typeSee whether the file's name and declared type match its real content.

Frequently Asked Questions