How to plot imported silhouettes instead of points in ggplot maps?

Question

I have a map with some points across it that were created with geom_point. They are in the exact location and color I need them to be, but I am trying to change the shape to a silhouette I imported from phylopic. Here is some sample data for the code

#Dataframe for the points
individual_dets = data.frame(longitude= seq(-64.5,-62.4,0.1),
                             latitude= seq(42.7,44.8,0.1),
                             year = sample(c(2016, 2017, 2018), 22, replace = T),
                             Zone = sample(c(1:4), 22, replace = T),
                             month = sample(month.abb, 22, replace = T))

Below is the code for my imported phylopic silhouette, and my code for the map with the points on it

library(rphylopic)
library(RCurl)
library(png)
library(mapdata)

#Import phylopic
rayurl = "http://phylopic.org/assets/images/submissions/a3b3e80c-22f2-4b8f-a3ac-42fe1583e0be.thumb.png"

raylogo = readPNG(getURLContent(rayurl))


#Importing the map
canada = map_data("worldHires", "Canada")

#The Map
ggplot() + 
  geom_polygon(data = canada, 
               aes(x=long, y=lat, group=group), 
               colour="grey50", fill = 'grey55')+
  #Coordinates I'm interested in looking at
  coord_sf(xlim=c(-64.5,-62.8), ylim=c(42.7,45)) +
  geom_point(data = individual_dets,
             aes(x = longitude,
                 y = latitude,
                 color = as.factor(Zone)),
             #fill = as.numeric(Zone)),
             size = 5) +
  scale_color_manual(values=c("#01579B", "#4FC3F7", "#ffa600", "#ff6361"), 
                     name = "Zone") 

Does anyone know how to take this saved silhouette and place it at the same coordinate and as the same color of my points?