WatermarkLocal draws the decoded source and text into a new Canvas whose dimensions equal the complete source frame. PNG, JPEG and WebP store that same composition differently. Preview and download use the same generated Blob, but no export is a byte-preserving edit of the original file.
Transparency separates PNG and JPEG
PNG preserves Canvas alpha and suits transparent assets. WebP may preserve alpha. JPEG has no alpha, so WatermarkLocal first fills transparent pixels with the selected matte, white by default. Text opacity is composited into every selected format.
A new file means new metadata and bytes
Canvas export does not deliberately carry EXIF, XMP, ICC, comments, source DPI or camera fields. JPEG and WebP quality changes compression and exact bytes. Compare the generated image visually in its destination and retain the original whenever metadata, colour management or provenance matters.
Keep a visible watermark in its proper scope
WatermarkLocal creates a newly encoded Canvas image. A visible text mark can be cropped, covered, edited or removed and does not prove copyright, ownership, consent, authenticity or tamper resistance. Use it for ordinary digital publishing only. Do not prepare identity, medical, legal, evidentiary, inspection, emergency, navigation or other safety-critical imagery, and independently verify every important result.