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forensics · jpeg · diff · local

Spot edits with Error Level Analysis

Re-save a JPEG at a known quality and visualise the per-pixel error. Edited or pasted regions usually pop out brighter than untouched areas.

Error Level Analysis
Source
—
no file
Quality
0.90
re-save
Amplify
×10
contrast
Status
—
local
Quality 0.90×10
input · image

image/jpeg · runs locally · nothing uploaded

output · preview
ELA diff appears here
Quick Start

How it works

Pick an image, tune the options, then download the result. Everything runs in your browser.

  1. 01

    Load a JPEG

    Only JPEGs work — the technique relies on JPEG compression error.

    Files stay in memory as an HTMLImageElement — the original bytes are never uploaded, and EXIF metadata is preserved until you explicitly transform it.

    jpeguploadcanvaslocaldecode
    input · bytesjpeg · loaded
    suspect.jpg
    loaded · decodedcanvas · ready
  2. 02

    Re-save it

    The tool re-encodes the image at the chosen quality (default 0.90).

    Encoder quality is exposed where the format supports it — JPEG and WebP get a 0–1 quality slider; PNG is lossless. Options re-render the canvas immediately.

    resaveoptionslive previewencoderquality
    q · tunable0.90 · live
    toBlob("image/jpeg", q)
    options applied · liveencoder · live
  3. 03

    Diff and amplify

    Per-pixel absolute difference is multiplied by your amplify factor.

    Pixel work runs on the Canvas 2D context — drawImage resamples with the browser’s bilinear filter and getImageData/putImageData back per-pixel passes.

    diffrenderCanvas 2Dpreviewpx-perfect
    amp · resampled×10 · px-perfect
    abs(orig - resaved) * amp
    preview · livepx-perfect
  4. 04

    Inspect the bright spots

    Cleanly compressed regions go dark; edited regions glow.

    Downloads ship via a hidden anchor with an object URL — no server round-trip, and the file on disk is untouched. The output filename inherits a sensible suffix.

    readdownloadblobclient-sideobject URL
    ok · blobready · saved
    Suspicious patch lit up
    analysed · ready to shipsuccess
Pro tips

Browser-only image work that scales

Convert with quality control

JPEG/WebP let you pick a 0–1 quality. Default 0.92 is a good compromise of size and visible quality.

PNG isn’t free

Use PNG only for transparency or sharp edges. For photos, WebP is smaller at the same perceived quality.

Strip EXIF for privacy

Photo EXIF often contains GPS, camera model, and timestamps. Strip before sharing public uploads.

Watch the colour profile

Convert to sRGB before web export. Wide-gamut images render oversaturated in non-managed browsers.

AVIF when it’s available

AVIF beats WebP on size at the same quality. Detect support via <picture> with fallbacks.

Lazy-load below the fold

Add loading="lazy" on <img>. The browser handles scheduling — no IntersectionObserver needed.

Related toolsImage Hex ViewerComparison SliderSteganography DecoderImage DiffEXIF ViewerHash Compare
Use Cases

When to use this tool

Common workflows it speeds up.

Photo forensics

Surface composited or healed regions in suspect photos. Decoded into a Canvas 2D context — original bytes never leave the tab, so you can process customer-uploaded photos, internal screenshots, or sensitive diagrams without privacy concerns.

px-perfect

Journalism

Spot-check submitted imagery for manipulation. Encoders expose quality 0–1 where the format supports it (JPEG, WebP); PNG and AVIF stay perceptually lossless. Pick 0.85 for web, 0.95 for archival, 0.7 for thumbnails.

quality-tunable

Insurance claims

Audit JPEG evidence for edits. Pair with the EXIF Stripper before sharing user-uploaded photos publicly. Camera serial numbers, GPS coordinates, and timestamps often hide in image metadata and leak more than the picture itself.

format-aware

OSINT

Quick visual triage of internet finds. Output preserves colour profile (sRGB) so it renders consistently across browsers, monitors, and print pipelines. Wide-gamut workflows can opt into Display P3 for modern Apple devices.

EXIF-safe

QA pipelines

Confirm originals haven't been re-encoded twice. Re-runs only on option changes, never on window resize, so the canvas stays responsive on large images. drawImage uses the browser's bilinear filter for fast resampling.

client-side

Education

Demonstrate JPEG compression artefacts. Downloads as .png, .jpg, .webp, or .avif with the correct MIME so editors apply native handling on save. The filename inherits a sensible suffix derived from the input.

compression-ready
FAQ

Frequently asked questions

ELA depends on JPEG's lossy compression. Re-saving a PNG produces no per-pixel error signal to compare against.
No. Bright regions are suspicious but not conclusive — sharp edges, text, and high-frequency content naturally glow.
0.88–0.95 is a good range. If your source was saved at quality Q, ELA at Q reveals the cleanest signal.
Multiplies the per-pixel difference so small errors become visible. Crank it up if the image looks too dark.
No. The image is re-encoded and diffed in your browser — it never leaves the device.
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