Local processing means the work can happen on your device
A browser tool can decode an image, draw it to a canvas, change dimensions and generate a new file without sending the original bytes to an application server. Similarly, some PDF and video operations can run in the browser, although performance and codec support vary by device.
This is a meaningful design choice, but it is not a universal privacy guarantee. A website can still load analytics, advertising, fonts or third-party scripts, which make their own network requests.
How to check the claim
Look for a clear privacy explanation and whether the feature requires account creation or cloud upload. Technically inclined users can open browser developer tools and inspect network requests while processing a non-sensitive sample file. A local Blob URL is not itself evidence that the file was uploaded.
Be cautious about assuming privacy from a lock icon alone. HTTPS protects transport; it does not establish where processing takes place.
Metadata can reveal more than pixels
Image files may contain camera settings, dates, editing-software identifiers, GPS coordinates or provenance-related markers. Not every format contains all of them, and absence of one label does not prove how an image was produced.
Before publishing a photograph, inspect metadata and decide what you want to keep. Cleaning metadata usually creates a new file and may alter quality, color information or authenticity-related records.
C2PA and provenance require careful wording
A file may contain metadata structures or markers associated with content provenance. Detecting a marker is not the same as validating a cryptographic signature or proving a particular author. Conversely, missing indicators do not prove an image was never edited or AI-generated.
Avoid tools that present simplistic “AI/not AI” claims based on a single metadata field.
What users can do
Keep originals, process copies, and open results to verify them. Do not publish sensitive files merely to test a tool. Read privacy and cookie notices, especially on pages carrying third-party advertising or analytics scripts.
For important legal, medical or identity documents, evaluate the tool carefully and consider an offline workflow with independently verified software.
A practical test with a harmless sample
Take a non-sensitive image and run one local tool while watching the browser's network panel. Distinguish requests for site scripts and ad resources from requests containing actual file bytes. A tool may fetch its JavaScript library from a CDN while still carrying out the image processing locally.
The HEIC conversion guide discusses why decoding support can vary by browser; our background removal guide explains why examining the exported pixels matters even when the processing location is known.
Limits of metadata cleaning
A copied file can retain sensitive information in the visible image, such as a street sign, badge or document number. Removing GPS metadata does not hide those visible details. Re-encoding can also remove useful timestamps or provenance information, so keep the source when authenticity matters.
A C2PA indicator and an independently verified signature are different things. Do not present a detected metadata marker as conclusive proof of authorship.