Example of how to combine plots with images side-by-side in cowplot for publication ready figures.

example_image_cowplot.R

library(png)
library(grid)
library(tidyverse)

# generate random data
my.data <- data.frame(x = c(1:10), y = rnorm(10))

# plot random data
g <- ggplot(my.data, aes(x = x, y = y)) + 
  geom_point()


# define plot png function 
plot_png <- function(fname){
  
  img <- readPNG(fname) %>% 
    rasterGrob(interpolate=FALSE)
  ggplot() +
    annotation_custom(img, xmin=-Inf, xmax=Inf, ymin=-Inf, ymax=Inf)
    
}

# create our ggplot-compatible png 
img <- plot_png("task.png")

# plot images together in grid
plot_grid(g, img, labels = letters)