Processing, 193 bytes

byte a[]=loadBytes("s.pde");noStroke();int x=0,y=0;for(int k=0;k<a.length%3;k++){append(a,byte(0));}for(int i=0;i<a.length-2;i+=3,x++){if(x>0){x=0;y+=1;}fill(a[i],a[i+1],a[i+2]);rect(x,y,1,1);}

Original

Resized

Even with Processing's builtins, this was very difficult.

Java 511 chars

The length of the solution leads to a greater picture which is cool, because these pictures are really nice.

import java.awt.image.*;import java.io.*;import java.nio.file.*;import javax.imageio.*; public class Q{public static void main(String[]a)throws Throwable{int w=19,h=9;byte[]e=Files.readAllBytes(Paths.get("Q.java"));String t=new String(e);while(t.length()%3!=0)t+='';BufferedImage I=new BufferedImage(w,h,BufferedImage.TYPE_INT_RGB);int r,c=r=0;for(int i=0;i<t.length();i++){I.setRGB(c,r,255<<24|t.charAt(i)<< 16|t.charAt(++i)<< 8|t.charAt(++i));if(++c==w){c=0;r++;}}ImageIO.write(I,"png",new File("Q.png"));}}

Note that there is an invisible trailing newline! It reads the source file, which has to be "Q.java" and creates a picture "Q.png" which looks like this:

or scaled 100x

PowerShell v4, 64 bytes

"P6 11 2 255"+[char[]](gc $MyInvocation.MyCommand.Name)|sc a.ppm

It gets the content of its own filename, casts the string as a char array, adds some PPM header and sets the content to a.ppm as output. 64 bytes makes it 11x2 pixels:

PHP, 226 bytes

Golfed

<?$b=strlen($w=join(file('p.php')));$z=imagecreatetruecolor(5,15);for($c--;++$c<$b+1|$i%3;$i%3?:$a=!imagesetpixel($z,$x%5,(int)$x++/5,$a))$a+=($c<$b?ord($w[$c]):0)*256**(2-$i++%3);header("Content-Type:image/png");imagepng($z);

Ungolfed version

<?
// Read the file into an array and join it together. Store the length of the resulting string.
$b=strlen($w=join(file('p.php')));

// Create the image. Our file is 226 bytes, 226/3 = 75 = 5 * 15
$z=imagecreatetruecolor(5,15);

// Loop through the script string, converting each character into a pixel.
// Once three characters have been converted, draw the pixel with the converted RGB value and reset the color to 0.
for($c--;++$c<$b+1|$i%3;$i%3?:$a=!imagesetpixel($z,$x%5,(int)$x++/5,$a))$a+=($c<$b?ord($w[$c]):0)*256**(2-$i++%3);

// Tell the program we're sending an image
header("Content-Type:image/png");

// And send it!
imagepng($z);

Enter this script into a file named 'p.php' and run it. You need your own method of running PHP script, because this reads from a local file.

Output image:

Node.js, 63 bytes

(F=x=>require('fs').writeFile('P6','P6 7 3 255 (F='+F+')()'))()

Outputs image into a file named P6 which is in the PPM (P6) format.

Here's a PNG rendition (7x3 pixels):

Python, 81 bytes

q=open(__file__).read()
print'P3n9 3 256 '+' '.join(map(lambda x:str(ord(x)),q))

Output is in PPM format.

This is what the image looks like:

Scaled up:

MATLAB, 81 72 69 bytes

@()image(shiftdim(reshape(evalin('base','char(ans)'),3,1,23)/255,1.))

This creates an anonymous function which can be pasted into the command window and run using ans(). When run this creates a 23-pixel image (a prime) therefore the most square representation is a simple array of pixels.

Explanation

When pasted into the command window, the anonymous function will automatically assign itself to the variable ans. Then from within the anonymous function, we use:

evalin('base', 'char(ans)')

which evaluates char(ans) within the namespace of the command window rather than within the local namespace of the anonymous function. It is therefore able to convert the anonymous function itself into a string representation.

Then we have the following operations which are more straightforward:

%// Reshape the result into a 3 x 1 x 23 matrix where the first dimension is RGB
%// due to column-major ordering of MATLAB
R = reshape(string, 3, 1, 23);

%// Divide the result by 255. This implicitly converts the char to a double
%// and in order for RGB interpreted properly by MATLAB, doubles must be
%// normalized between 0 and 1.
R = R / 255;

%// Shift the dimensions to the left 1 to move the RGB channel values into
%// the third dimension. Note the extra decimal point. This is because it
%// is far shorter to lengthen the code by one byte than to pad the string
%// to give us a length divisible by 3
R = shiftdim(R, 1.);

%// Display the RGB image
image(R);

Javascript ES6 - 216 bytes

f=(  )=>((d=(x=(v=document.createElement`canvas`).getContext`2d`).createImageData(v.width=9,v.height=8)).data.set([..."f="+f].reduce((p,c,i)=>(c=c.charCodeAt(0),[...p,...i%3<2?[c]:[c,255]]))),x.putImageData(d,0,0),v)

Ungolfed:

f=(  )=>(                                           // define function f (extra spaces to account for missing pixel + alpha channel calculation)
 (d=(x=(v=document.createElement`canvas`).          // assign html5 canvas to v
          getContext`2d`).                          // assign graphics context to x
          createImageData(v.width=9,v.height=8)).   // create & assign ImageData to d
                                                    //   set width and height of both d and v
 data.set([..."f="+f].                              // get f's source, convert to array of chars
   reduce((p,c,i)=>(c=c.charCodeAt(0),              // convert char array to int array
                    [...p,...i%3<2?[c]:[c,255]]))), // insert alpha values 255
 x.putImageData(d,0,0),                             // draw source RGBA array to canvas
 v)                                                 // return canvas

Note: f returns a canvas.

Example run (assumes there's a <body> to append to):

document.body.appendChild(f())

Should dump the following image to the page (enlarged):

APL (Dyalog), 33 bytes

Requires ⎕IO←0 which is default on many systems. Also, AutoFormat should be off to preserve the program exactly as given.

(⊂⎕NPUT⊃)'P',⍕⎕AV⍳'␍ɫ␉⍣',⊃⌽⎕NR'f'  

Hex _{^{B9 BA FD 4E 50 55 54 BB F8 0D 50 0D C2 CD FD 41 56 B2 0D 03 0B 01 FF 0D C2 BB C8 FD 4E 52 0D 16 0D}}
Unicode _{^{28 2282 2395 4E 50 55 54 2283 29 27 50 27 2C 2355 2395 41 56 2373 27 0D 026B 08 2363 27 2C 2283 233D 2395 4E 52 27 66 27}}

Creates P: _{^{P3 11 1 255 185 186 253 78 80 85 84 187 248 13 80 13 194 205 253 65 86 178 13 3 11 1 255 13 194 187 200 253 78 82 13 22 13}}
Which you save and drop here to see:

⎕NR'f' Nested Representation of the program f

⊃⌽ pick the last (lit. first of the reversed) element (line)

'␍ɫ␉⍣', prepend the four characters (filetype, width, height, max)

⎕AV⍳ find corresponding indices in the Atomic Vector (the character set

⍕ format as text

'P', prepend a letter

(…) apply the following tacit function:

 ⊂ take the entire argument [and into a]

 ⎕NPUT Native [file,] Put [it, with a filename consisting of]

 ⊃ the first character ("P")

Javascript(ES6) 324 312 309 Bytes

I'm sure this could be golfed a bit:

f=()=>{s="f="+f;l=s.length/3;c=document.createElement('canvas');for(i=0;++i<l/i;l%i?0:w=i,h=l/w);c.s=c.setAttribute;c.s("width",w);c.s("height",h);(i=(t=c.getContext('2d')).createImageData(w,h)).data.map((a,b)=>i.data[b]=b%4<3?s.charCodeAt(b-~~(b/4)):255);t.putImageData(i,0,0);open(c.toDataURL('image/png'))}

• creates a canvas
• builds image in it
• Opens data url for image in new tab

New lines for readability:

f=()=>{
    s="f="+f;l=s.length/3;
    c=document.createElement('canvas');
    for(i=0;++i<l/i;l%i?0:w=i,h=l/w);
    c.s=c.setAttribute;
    c.s("width",w);
    c.s("height",h);
    (i=(t=c.getContext('2d')).createImageData(w,h)).data.map((a,b)=>i.data[b]=b%4<3?s.charCodeAt(b-~~(b/4)):255);
    t.putImageData(i,0,0);
    open(c.toDataURL('image/png'))
}

Output