Watermark Anchor
mark-anchor
The mark-anchor parameter chooses which point of the watermark an explicit mark-x and mark-y land on. The default is the watermark’s top-left corner, which is how positioning has always worked.
Centering a badge at a point used to mean subtracting half its size from the coordinates by hand, which only works if you know the badge’s rendered size. mark-anchor=center does it for you.
The value is either an alignment keyword — center, bottom,right, top, and so on — or a pair of fx,fy fractions, where 0,0 is the top-left of the watermark and 1,1 its bottom-right.
mark-anchor is only read when mark-x or mark-y is set — it has nothing to act on under mark-align alone. It is ignored under mark-tile=grid.
Writing the coordinates as decimals makes them relative lengths, so mark-x=0.7&mark-y=0.3&mark-anchor=center holds its position at every output width.