title: Is there a way to add an alpha value within geom_image in ggplot?
body: <p>I am currently trying to create a plot that has logos mapping to X and Y coordinates. The goal though is have another set of points with the same logos, but with an alpha value so that the logos are more transparent. </p>
  
  <p>Here is a reproducible example. The goal is to have the logos on the left be transparent.</p>
  
  <pre><code>library(ggimage)
  library(tidyverse)
  library(RCurl)
  
  Sample_X1 &lt;- c(1,0,2,3,1)
  Sample_X2 &lt;- c(4,5,7,4,3)
  Sample_Y &lt;- c('A','B','C','D','E')
  Logo &lt;- 'https://i1.pngguru.com/preview/233/348/954/numix-circle-for-windows-rstudio-icon-png-icon-thumbnail.jpg'
  
  data &lt;- data.frame(cbind(Sample_X1, Sample_X2, Sample_Y, Logo))
  
  ggplot(data = data) +
    geom_segment(aes(x = Sample_X1, xend = Sample_X2, y = Sample_Y, yend = Sample_Y), size = 1) +
    geom_image(aes(x = Sample_X1, y = Sample_Y, image = Logo), size = .05) +
    geom_image(aes(x = Sample_X2, y = Sample_Y, image = Logo), size = .05) +
    theme_minimal() +
    labs(title = 'Example for Stack Overflow')
  </code></pre>
  
  <p><img src="https://i.stack.imgur.com/YfXiq.png" alt="Sample Output"></p>
  
  <p>Is there a way to accomplish this with ggplot? So far I have only been able to find ways to make background logos transparent, but they aren't able to be mapped to the XY data. </p>
  
  <p>Any help is appreciated!</p>