Ttgjyuk

To extend @snow's answer, put the code below from the very first line of your .bashrc. And be proud to be ubuntu user :)

echo "MMMMMMMMMMMMKlxMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMW0occlxNM"
echo "MMMMMMMMMMMMOcxMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMKOXMMMMMMMMMMMMMMMMMNdcoxkOlc0"
echo "MMMMMMMMMMMMOcxMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMdcOMMMMMMMMMMMMMMMMMkoO0lckkcl"
echo "dxWMMMM0d0MMOcoxdooxONMMMOdXMMMMXdkMMWkxdoodxONMMMdcldddkMXdxWMMMM0dKM0coOxk0xcd"
echo "ccNMMMMxckMMOco0XNXkclKMMxc0MMMMKcoMMNllKXXXkclXMMdcxKKKXMKclNMMMMkc0MM0oclldokN"
echo "ccNMMMMxckMMOcxMMMMMOclWMxc0MMMMKcoMMNllWMMMMdcOMMdcOMMMMMKclNMMMMkc0MMMMNXXNWMM"
echo "ccNMMMMxckMMOcxMMMMMKccNMxc0MMMMKcoMMNllWMMMMxckMMdcOMMMMMKclNMMMMkc0MMMMMMMMMMM"
echo "lcKMMMMxckMMOcxMMMMWdcxMMkcxMMMMKcoMMNllWMMMMkckMMxckMMMMMNccKMMMMkc0MMMMMMMMMMM"
echo "0lcxkkklckMMOclkOkxlckWMMNocdkkkdcoMMNllWMMMMkckMMXlcxkkxNM0lcxkkkoc0MMMMMMMMMMM"
echo "MNxlccloxXMMXxolccokNMMMMMWOolclox0MMWxkWMMMM0d0MMMXxlclxNMMNklcclokXMMMMMMMMMMM"

OR

echo " _ _ "
echo " _ _| |__ _ _ _ __ | |_ _ _ "
echo "| | | | '_ | | | | '_ | __| | | |"
echo "| |_| | |_) | |_| | | | | |_| |_| |"
echo " __,_|_.__/ __,_|_| |_|__|__,_|"

The secret to these image like characters is to use an image converter to ASCII characters. There are lots of free tools in the wild like toilet or figlet but I personally use jp2a.

You can also use this site for generating text to ASCII instead of image to ASCII.

How do we apply ASCII art into the terminal?

There are numerous ways of generating ASCII art, including specialized software and manual building, but, there are also web-sites that generate ASCII art by simply entering the desired name.
first, we need to generate/create the ASCII "code": visit this web-site, type a desired name and copy the "live" generated ASCII result
then, create a text file named art and paste into it the above mentioned generated ASCII result
copy the art file in your home folder (navigate here by clicking Nautilus sidebar's Home)
open the .bashrc file (to make it viewable, press Ctrl+H) and paste on the bottom of the page

cat art

Worth mentioning:

The above mentioned site contains hundreds of different fonts for generating ASCII that feature various sizes, 3D-look, etc.

Source

As for images to ascii go to this website

First generate a ascii drawing. I recommend asciio:

apt-get install asciio

Example:

 .-------.
 | Hi |
 '-------'
 ^ (_/)
 '----- (O.o)
 (> <)

Copy and paste the drawing in file:

vim /home/<youruser>/banner

Finally, add at the end of file to read when you open a new bash:

echo "cat banner" >> /home/<youruser>/.bashrc

Open another terminal:

You can add interesting ASCII arts on your terminal without leaving your terminal. cowsay has some of the coolest ASCII arts and piping fortune outputs into cowsay can take this to another level. Lets see how this is done, open your terminal and type:

sudo apt-get install cowsay

Now cowsay is installed lets have some fun, add following command

cowsay I am in a good mooooo-d.

If you don't like the cow, there is a mystical zoo within your terminal, type

cowsay -f dragon Who dared to wake me up?

To bring up list of all the animals in your mystical zoo type cowsay -l.
If you prefer 'thinking animal' over talking one try

cowthink -f <animal name> <your message>

< > are to be ignored. If you want to display same custom message each time you login please continue, otherwise skip to next step.

Copy your ASCII art and go to home directory. Create a file
<newfile.txt>, paste your ASCII art inside the file and save it.
Open a file.bashrc from home directory. Add the following on bottom
line of the file and save it.

cat <newfile.txt>

You are done :) reopen your terminal.

Lets make your animal a little more intelligent by adding fortune

sudo apt-get install fortune

Go to home directory and open .bashrc and add the following as top line of the file

fortune | cowsay -f <your animal>

Now save the file and you are done :)

This one takes a png image file and outputs a facsimile onto your terminal

If you have nodejs installed then issue

npm install -g picture-tube

then put this into bottom of your ~/.bashrc

echo "picture-tube --cols 60 /tmp/justpng/orbifold_333_shell.png"
 picture-tube --cols 60 /tmp/justpng/orbifold_333_shell.png

code is at https://github.com/substack/picture-tube

enjoy

sudo apt-get install figlet

echo "Hello world!" | figlet | color_it.sh 54

cat color_it.sh

#!/usr/bin/env bash 

## A.M.Danischewski 2015+(c) Free - for (all (uses and 
## modifications)) - except you must keep this notice intact. 

declare INPUT_TXT=""
declare ADD_LF="n" 
declare -i DONE=0
declare -r COLOR_NUMBER="$1:-247"
declare -r ASCII_FG="\033[38;05;"
declare -r COLOR_OUT="$ASCII_FG$COLOR_NUMBERm"

function show_colors() 
 ## perhaps will add bg 48 to first loop eventually 
 for fgbg in 38; do for color in 0..256 ; do 
 echo -en "\033[$fgbg;5;$colorm $colort\033[0m"; 
 (($(($color+1))%10==0)) && echo; done; echo; done
 

if [[ ! $# -eq 1 || $1 =~ ^-. ]]; then 
 show_colors 
 echo " Usage: $0##*/ <color fg>" 
 echo " E.g. echo "Hello world!" | figlet | $0##*/ 54" 
else 
 while IFS= read -r PIPED_INPUT || DONE=1; ADD_LF=""; ; do 
 PIPED_INPUT=$(sed 's#\#\\#g' <<< "$PIPED_INPUT")
 INPUT_TXT="$INPUT_TXT$PIPED_INPUT$ADD_LF"
 (($DONE)) && break; 
 done
 echo -en "$COLOR_OUT$INPUT_TXT\033[00m"
fi 

its typical to create a dir ~/bin and make all those files visible

mkdir ~/bin
# ... put above color_it.sh as file ~/bin/color_it.sh
chmod +x ~/bin/color_it.sh # make it executable
export PATH=$HOME/bin:$PATH # add this line to your ~/.bashrc

echo "Hello world!" | figlet | color_it.sh 34