require(png)
require(grid)

## select the PNG file
z <- readPNG(file.choose())

## Function to draw your statement
copyright.draw <- function(label, image, x, y, size, ...) {
  lab <- textGrob(label = label,
    x = unit(x, "npc"), y = unit(y, "npc"),
    just = c("left", "centre"), gp = gpar(...))
  logo <- rasterGrob(image = image,
    x = unit(x, "npc") + unit(1, "grobwidth", lab), y = unit(y, "npc"),
    width = unit(size, "cm"), height = unit(size, "cm"),
    just = c("left", "centre"), gp = gpar(...))
  grid.draw(lab)
  grid.draw(logo)
}

plot(1:10, 1:10)
copyright.draw("Copyright statement ", z, .02, .04, .5, fontsize = 8)