image_modify_local: Modify Only a Subregion of an Image
In plothelper: New Plots Based on 'ggplot2' and Functions to Create Regular Shapes

The function allows you to modify a subregion of your image (or, the opposite, keep the subregion unchanged while modifying other parts). You can set the four sides of the subregion or an irregular polygon by mouse click. If it is irregular, you MUST click in order.

image_modify_local(
  x,
  FUN,
  geometry = "click",
  local = "local",
  rectangle = TRUE,
  trim = FALSE,
  ...
)

`x`	an image read into R by `magick::image_read` or an image modified by functions in the magick package.
`FUN`	the function used to modify `x`. NOTE: the result of `FUN` must be of the same class as `x` and its width and height must not be changed during modification.
`geometry`	this parameter is different from the one used in package magick. Here, in this function, you can set `geometry = "click"` if you want to show which part you want to modify by mouse click (see function `image_crop_click` for how to use mouse click). Otherwise, you can use a length 4 vector with the exact order: left, right, top, bottom.
`local`	if it is 1 or "local", only a subregion of your image will be modified. If it is 2 or "other", keep the subregion unchanged while modifying other parts. If it is 3 or "subregion", the result is only the modified subregion, not the whole image.
`rectangle`	if it is TRUE (default), the subregion is a rectangle. If it is FALSE, the subregion can be an irregular polygon designated by your mouse click.
`trim`	whether to trim the subregion. This is only used when `local` is 3 or "subregion". It helps remove the transparent parts. See `image_crop_click` to know how to use this parameter.
`...,`	extra parameters used by `FUN`.