I have a dirty working tree, dirty because I made changes to source files and touched up some images. I was trying to add just the images to the index, so I ran this command:

git add *.png

But, this doesn't add the files. There were a few new image files that were added, but none of the ones that were modified/pre-existing were added.

What gives?

Edit: Here is some relevant terminal output

$ git status
# On branch master
#
# Changed but not updated:
#   (use "git add <file>..." to update what will be committed)
#   (use "git checkout -- <file>..." to discard changes in working directory)
#
#   modified:   src/main/java/net/plugins/analysis/FormMatcher.java
#   modified:   src/main/resources/icons/doctor_edit_male.png
#   modified:   src/main/resources/icons/doctor_female.png
#
# Untracked files:
#   (use "git add <file>..." to include in what will be committed)
#
#   src/main/resources/icons/arrow_up.png
#   src/main/resources/icons/bullet_arrow_down.png
#   src/main/resources/icons/bullet_arrow_up.png
no changes added to commit (use "git add" and/or "git commit -a")

Then executed "git add *.png" (no output after command)

Then:

$ git status
# On branch master
#
# Changes to be committed:
#   (use "git reset HEAD <file>..." to unstage)
#
#   new file:   src/main/resources/icons/arrow_up.png
#   new file:   src/main/resources/icons/bullet_arrow_down.png
#   new file:   src/main/resources/icons/bullet_arrow_up.png
#
# Changed but not updated:
#   (use "git add <file>..." to update what will be committed)
#   (use "git checkout -- <file>..." to discard changes in working directory)
#
#   modified:   src/main/java/net/plugins/analysis/FormMatcher.java
#   modified:   src/main/resources/icons/doctor_edit_female.png
#   modified:   src/main/resources/icons/doctor_edit_male.png