Image MIME Reference
JPEG
JPEG Image
image/jpeg
VS
Progressive JPEG (Legacy IE Alias)
image/pjpeg
PJPEG
A complete technical comparison of JPEG Image and Progressive JPEG (Legacy IE Alias) — covering compression, feature support, browser compatibility, magic bytes, and when to choose each format.
Equal browser support
Feature Support
| Feature | JPEG | PJPEG |
|---|---|---|
| Transparency (Alpha) | ✕ No | ✕ No |
| Animation Support | ✕ No | ✕ No |
| Progressive Loading | Yes | Yes |
| HDR Support | ✕ No | ✕ No |
| EXIF Metadata | Yes | Yes |
| ICC Color Profile | Yes | Yes |
JPEG Image
image/jpeg
Extension
.jpg.jpeg.jpe.jfif
Container
JFIF / Exif
Compression
Lossy
Algorithm
DCT (Discrete Cosine Transform)
Color Depth
8-bit
Developed by
Joint Photographic Experts Group
Released
1992
Magic Bytes
FF D8 FF
Progressive JPEG (Legacy IE Alias)
image/pjpeg
Extension
.jpeg.jpg.pjpeg.pjp.jfif
Container
JPEG (ISO/IEC 10918-1)
Compression
Lossy (DCT)
Algorithm
Discrete Cosine Transform (DCT)
Color Depth
8-bit, 12-bit
Developed by
Joint Photographic Experts Group / Microsoft (Alias)
Released
1992
Magic Bytes
FF D8 FF E0 (JFIF) / FF D8 FF E1 (Exif)
Browser Support Comparison
| Browser | JPEG | PJPEG |
|---|---|---|
Chrome
|
✓ All
|
✓ All
|
Firefox
|
✓ All
|
✓ All
|
Safari
|
✓ All
|
✓ All
|
Edge
|
✓ All
|
✓ All
|
IE (Legacy)
|
✓
|
✓
|
JPEG
JPEG Strengths
- Universal support — every browser, OS, and application handles JPEG
- Excellent compression for complex photographs with natural color gradients
- Rich metadata support: EXIF (GPS, camera settings), ICC color profiles
Limitations
- No transparency — cannot have a transparent background
- Lossy compression introduces visible artifacts on sharp edges and text
- No animation support
PJPEG
PJPEG Strengths
- Progressive JPEGs (which this MIME type attempted to describe) provide excellent perceived loading speeds on slow connections by rendering a low-resolution preview first
- Files sent with this MIME type are fully backwards compatible with any standard JPEG decoder
Limitations
- It is a non-standard MIME type that violates IANA specifications
- Causes strict file upload validation scripts to fail if not explicitly whitelisted or mapped
- Creates unnecessary confusion, as the official image/jpeg MIME type already fully encompasses progressive encoding
When to choose which format
JPEG
Use JPEG when…
- Photography
- Websites
- Social Media
PJPEG
Use PJPEG when…
- Legacy Internet Explorer File Uploads
- Progressive Image Rendering (Historical context)