What you like to do ... there is a working SSH / SSL already on your Mac. If you like to build stunnel you need Xcode with the CLI tools ... and some time. I haven´t tried it but a quick look in the build instructions looks as if there are no big problems.
As promised, here are the steps to build stunnel from source. I used a Lion machine but it is the same on a Mountain Lion machine. There is no need for Fink, MacPorts or Homebrew ... brings more troubles then it helps.
Go to https://www.stunnel.org/downloads.html and download stunnel-5.23.tar.gz and stunnel-5.23.tar.gz.sha256. Open a terminal Utilities => Terminal>. Terminal is case sensitive, before you do something think twice before you press return - there is no undo or redo in terminal. Each line is one line in terminal and needs to press return at the end of the line.
cd $HOME/Downloads
openssl dgst -sha256 stunnel-5.23.tar.gz
more stunnel-5.23.tar.gz.sha256
Compare the output of the last 2 lines - if it matches all is fine, if not you had a security problem during download.
tar -xzvf stunnel-5.23.tar.gz
cd stunnel-5.23
./configure && make && make check && sudo make install
The configure script uses autoconf, so put your fingers away from other options because if all is there and supported it will build a fine 64 bit app for you. make check is optionally. sudo make install requires your admin password. During this step you had to input some basic informations (self explaining). The && is used to run one command after each other ONLY if the last was successful.
After all is done your stunned app was installed in /usr/local/bin. To run it, open terminal and type stunnel or stunnel3 (see the docs for the difference) and press return.
For the config file type in terminal.
cd /usr/local/etc/stunnel
sudo cp stunnel.conf-sample stunnel.conf
sudo pico stunnel.conf
For the documentation of pico use in terminal.
man pico
If I had some mistypes of filenames or anything else here use in terminal the following command to list a directory
ls -la
For the rest, have fun with stunned and the documentation of it !
It's stored in an extended attribute on the file. Specifically the com.apple.metadata:kMDItemWhereFroms attribute. It may stay with the file when you move it to different computers, but it depends on the filesystem or file sharing protocol you use. If you move it to another Mac on an HFS+ disk, it will likely keep it, but not necessarily if you transfer over the network, and most likely not with an external disk with a non-HFS+ filesystem.
You can check a file by running xattr -lp com.apple.metadata:kMDItemWhereFroms myfile in the Terminal, or remove it with xattr -d com.apple.metadata:kMDItemWhereFroms my file. ls -l@ flag is also useful; it will list the names of xattrs along with the usual ls information.
If you want to remove it from multiple files, have a look at this question: How to remove xattr com.apple.quarantine from all .webarchive files with that extended attribute?
Best Answer
On my machine (running 10.8.3), it is in
/Applications/Utilities/Grab.app.You can search for this using Spotlight: press cmd-space or click the magnifying glass near top right in the menu bar.
There are also some key shortcuts that save (or copy to the clipboard) images from the screen, clipped in various ways. cmd-shift-4 is one I use regularly, but there are several variants on this.