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png is from http://www.flaticon.com/packs/communication-and-media-2



set.seed(123)

files = list.files("example/png/", full.names = TRUE)
library(png)
library(circlize)

circos.initialize(fa = letters[1:20], xlim = c(0, 1))
circos.track(ylim = c(0, 1), panel.fun = function(x, y) {
    f = sample(files, 1)
    image = as.raster(readPNG(f))

    circos.raster(image, CELL_META$xcenter, CELL_META$ycenter,
        width = "1cm", height = "1cm", facing = "downward")
})
circos.clear()