Yes it's possible to do this in perl, as the others have already suggested.

If you didn't know then it might be worth looking at the command line tools from the imagemagick suite.

For example I wrote a console application to dump out images from my webcam to a file "foo.jpg" and then I call that in a shellscript to add some text to it:

# Get a temporary file
camgrab -device "/dev/video" -output /tmp/image.jpg

# Add the date to the bottom of the image.
convert -font helvetica -fill black -draw "text 10, 280 '`date`'" /tmp
+/image.jpg /tmp/image.jpg
[download]

This isn't exactly what you're looking for as I am adding text to an image, but you can overlay other images too "man convert" will give you the details.