How do I get annotation_custom() grob to display along with scale_y_reverse() using R and ggplot2?

Question

I'm new to ggplot2 and relatively new to R. I can make a picture appear on a plot, and I can make the y axis reverse scale, but I don't know how to do both at once. For example:

library(ggplot2)

y=c(1,2,3)
x=c(0,0,0)
d=data.frame(x=x, y=y)

#following http://stackoverflow.com/questions/9917049/inserting-an-image-to-ggplot2/9917684#9917684
library(png)
library(grid)
img <- readPNG(system.file("img", "Rlogo.png", package="png"))
g <- rasterGrob(img, interpolate=TRUE)

#these work fine - either reversing scale, or adding custom annotation
ggplot(d, aes(x, y)) + geom_point()
ggplot(d, aes(x, y)) + geom_point() + scale_y_reverse()
ggplot(d, aes(x, y)) + geom_point() + annotation_custom(g, xmin=.23, xmax=.27, ymin=1.8, ymax=2.2)

#these don't...combining both reverse scale and custom annotation
ggplot(d, aes(x, y)) + geom_point() + annotation_custom(g, xmin=.23, xmax=.27, ymin=1.8, ymax=2.2) + scale_y_reverse()
ggplot(d, aes(x, y)) + geom_point() + annotation_custom(g, xmin=.23, xmax=.27, ymin=2.2, ymax=1.8) + scale_y_reverse()

I'm sure I'm missing something pretty basic. Where should I start looking both to get my little graphic to display on a reverse scale plot, and also to understand things better under the hood?

CLARIFICATION IN RESPONSE TO COMMENTS: The example above is me trying to simplify the problem I'm having. I don't know if it matters, but I'm not merely trying to overlay some data on a static image. I actually want to place an image in a certain spot on a plot, based on the data in the plot. However, I can't seem to do that when the axis scale is reversed. And, as it turns out, I can't even put an image in an absolute position when the scale is reversed either, so that's the code example I posted.

Answer 1

With scale_y_reverse, you need to set the y coordinates inside annotation_custom to their negative.

library(ggplot2)
y=c(1,2,3)
x=c(0,0,0)
d=data.frame(x=x, y=y)


library(png)
library(grid)
img <- readPNG(system.file("img", "Rlogo.png", package="png"))
g <- rasterGrob(img, interpolate=TRUE)

ggplot(d, aes(x, y)) + geom_point() + 
   annotation_custom(g, xmin=.20, xmax=.30, ymin=-2.2, ymax=-1.7) + 
   scale_y_reverse()

Why negative? The y coordinates are the negative of the original. Check out this:

(p = ggplot(d, aes(x=x, y=y)) + geom_point() + scale_y_reverse())
y.axis.limits = ggplot_build(p)$layout$panel_params[[1]][["y.range"]]
y.axis.limits

OR, set the coordinates and size of the grob in relative units inside rasterGrob.

g <- rasterGrob(img, x = .75, y = .5, height = .1, width = .2, interpolate=TRUE)

ggplot(d, aes(x, y)) + geom_point() + 
   annotation_custom(g) +
   scale_y_reverse()