ImageScaled

ImageScaled[{x,y}] gives the position of a graphical object in terms of coordinates scaled to run from 0 to 1 across the whole image region in each direction.

ImageScaled[{dx,dy},{x0,y0}] gives a position obtained by starting at ordinary coordinates {x0,y0}, then moving by an image-scaled offset {dx,dy}.

Examples

Place text at the center of a graphic:

Graphics[{Circle[], Text["Center", ImageScaled[{0.5, 0.5}]]}]

Please visit the official Wolfram Language Reference for more details.