I would like to map OHS incidents over a PNG of a hospital site plan using ggplot2. I tried reading this non-geographic map as ggimage.

So far, I have tried the following with the observations (14462) that I have.
Data set example
toy <- data.frame(patient_ID = c(1001,1001,1002,1003,1004),
SEX = c("M","M","F","F","F"),
phenotype = c("Psychiatric","Psychiatric", "Cardio",
"Cancer","Psychiatric"),
x = c(0.5737, 0.5737, 0.6968, 0.4704, 0.6838),
y= c(0.3484, 0.3484, 0.62, 0.5216, 0.2486))
I tried reading the file as a raster and then using ggmaps, but the difficulty is not a legend.
library(ggmap)
library(png)
library(ggplot2)
library(data.table)
toy <- fread("toy.csv")
# read in image
r <- readPNG("ICU-crop.png")
#use ggimage to convert to plot and add gender
ggimage(r, scale_axes = TRUE) +
geom_point(aes(x = x, y = y, colour = SEX), data = toy,
size = I(1), fill = NA)
I would really like to use ggplot, but you need a legend. I'm not sure what other methods I can use for ggplot over PNG.