WatermarkLocal uses nine fixed anchors: three horizontal choices crossed with three vertical choices. A top-left mark starts at the chosen margin from both edges; a bottom-right mark ends at the margin; a centered mark uses the exact source midpoint. This rule is deterministic for every image size and avoids a hidden drag position that is hard to reproduce.
Margin is measured in source pixels
A 24 px margin means 24 decoded image pixels, not 24 CSS display pixels. On a large source the preview scales down, but export still uses the requested source value. Center positions ignore the edge margin because neither axis is attached to an edge.
Large or rotated text can clip
The tool does not silently shrink or move text. If size, rotation or margin sends part of the line beyond the frame, the preview shows that clipping and export keeps it. Reduce size, angle or margin after checking the actual composition.
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.