Is it possible to create a multiplot of data and images with ggplot?

Question

I would like to know if it is possible with ggplot2 to create a multiple plot (like a facet) including images to look like that:

I don't know exactly how to arrange the image data to pass them to geom_raster() or how to include an image in a data frame...

what I have tried:

> img1 <- readPNG('1.png')
> img2 <- readPNG('2.png')
> img3 <- readPNG('3.png')

> test <- data.frame(c(1,2,3),c(5,2,7),c(img1,img2,img3))
> nrow(test)
 [1] 4343040

I already have a problem here to build a data frame with the images inside... each 3 lines a repeated (I guess once per pixel).

Answer 1

I went finally with this solution which decompose the plot to a gtable, add one more line and insert images. Of course once decompose one can't add more layer to the plot, so it should be the very last operation. I don't think the gtable can be converted back to plot.

library(png)
library(gridExtra)
library(ggplot2)
library(gtable)
library(RCurl) # just to load image from URL

#Loading images
img0 <- readPNG(getURLContent('http://i.stack.imgur.com/3anUH.png'))
img1 <- readPNG(getURLContent('http://i.stack.imgur.com/3anUH.png'))

#Convert images to Grob (graphical objects)
grob0 <- rasterGrob(img0)
grob1 <- rasterGrob(img1)

# create the plot with data
p <- ggplot(subset(mpg,manufacturer=='audi'|manufacturer=='toyota'),aes(x=cty,y=displ))+facet_grid(year~manufacturer)+geom_point()

# convert the plot to gtable
mytable <- ggplot_gtable(ggplot_build(p))

#Add a line ssame height as line 4 after line 3
# use gtable_show_layout(mytable) to see where you want to put your line
mytable <- gtable_add_rows(mytable, mytable$height[[4]], 3)
# if needed mor row can be added 
# (for example to keep consistent spacing with other graphs)

#Insert the grob in the cells of the new line
mytable <- gtable_add_grob(mytable,grob0,4,4, name = paste(runif(1)))
mytable <- gtable_add_grob(mytable,grob1,4,6, name = paste(runif(1)))

#rendering
grid.draw(mytable)

Note: In this example, I use twice the same image, but it is of course possible to have as much as needed.

Inspired by: How do you add a general label to facets in ggplot2?