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}.

MORE INFORMATION

ImageScaled can be used to specify scaled coordinates in any two-dimensional graphics primitive.

You can use ImageScaled to represent objects that occupy a fixed region in the image associated with a graphic.

The image region used to define ImageScaled includes only the region in which the graphic can actually be drawn. It does not include empty space arising from mismatches in shape between ImageSize and AspectRatio, or defined by ImageMargins.