Create an SVG based on the brightness of an image transformed into sine waves. Simple UI to control effects. Saved SVG is larger than original image for detail.

SquiggleDraw.pde

import controlP5.*;
import processing.svg.*;

ControlP5 gui;

PShape s;
PShape liner;

PImage p1;
PImage p2;


int ystep = 160;//80;
int ymult = 6;//5;
int xstep = 3;

int imageScaleUp = 3;

float r = 0.0;
float a = 0.0;

float startx,starty;

int b,oldb;

boolean isRunning = true;
boolean isRecording = false;
boolean needsReload = true;

boolean invert = false;

String imageName = "kitten.jpg";//"IMG_6887bw.png";//"kitten-1.jpg";//"pluto.jpg";

void setup() {
  size(100,100);
  loadMainImage(imageName);
  createSecondaryImage();

  gui = new ControlP5(this);
  gui.addSlider("sldLines").setSize(130,30).setCaptionLabel("Number of Lines").setPosition(10,20).setRange(10,200).setValue(120).setColorCaptionLabel(color(0));
  gui.getController("sldLines").getCaptionLabel().align(ControlP5.LEFT, ControlP5.TOP_OUTSIDE);

  gui.addToggle("tglInvert").setCaptionLabel("Invert Colors").setPosition(10,80).setValue(false).setMode(ControlP5.SWITCH).setColorCaptionLabel(color(0));
  gui.getController("tglInvert").getCaptionLabel().align(ControlP5.LEFT, ControlP5.TOP_OUTSIDE);

  gui.addSlider("sldAmplitude").setSize(130,30).setCaptionLabel("Squiggle Strength").setPosition(10,140).setRange(0,20).setValue(5).setColorCaptionLabel(color(0));
  gui.getController("sldAmplitude").getCaptionLabel().align(ControlP5.LEFT, ControlP5.TOP_OUTSIDE);

  gui.addSlider("sldXSpacing").setSize(130,30).setCaptionLabel("Detail").setPosition(10,200).setRange(1,30).setValue(27).setColorCaptionLabel(color(0));
  gui.getController("sldXSpacing").getCaptionLabel().align(ControlP5.LEFT, ControlP5.TOP_OUTSIDE);

  gui.addBang("bangSave").setSize(130,30).setCaptionLabel("Save SVG").setPosition(10,300).setColorCaptionLabel(color(255));
  gui.getController("bangSave").getCaptionLabel().align(ControlP5.CENTER, ControlP5.CENTER);

  smooth();
  background(255);
  shapeMode(CORNER);
}

void loadMainImage(String inImageName) {
  p1 = loadImage(inImageName);
  surface.setSize(p1.width + 150, p1.height);

  // filter image
  p1.filter(GRAY);
  p1.filter(BLUR,2);
  if (invert) {
    p1.filter(INVERT);
  }
}

void createSecondaryImage() {
  p2 = createImage(p1.width*imageScaleUp,p1.height*imageScaleUp,RGB);
  p2.copy(p1,0,0,p1.width,p1.height,0,0,p1.width*imageScaleUp,p1.height*imageScaleUp);
}

void draw() {
  if (isRunning) {
    if (isRecording) {
      beginRecord(SVG, "squiggleImage_" + millis() + ".svg");
    }
    createPic();
    if (isRecording) {
      endRecord();
    }
    isRunning = false;
    isRecording = false;
    createPic();
  }
}

void createPic() {

  if (needsReload) {
    loadMainImage(imageName);
    createSecondaryImage();
    needsReload = false;
  }
  
  stroke(0);
  noFill();
  
  startx = 0.0;
  starty = 0.0;

  s = createShape(GROUP);

  for (int y=0;y<p2.height;y+=p2.height/ystep) {
    
    liner = createShape(PShape.PATH);
    liner.beginShape();
    a = 0.0;
    startx = 0;
    
    b = (int)brightness(p2.get(1,y));
    float z = 255.0-b;
    r = 5;
    starty = y + sin(a)*r;
    
    liner.vertex(startx,starty);
    
    for (int x = 0;x<p2.width;x+=xstep) {
      b = (int)brightness(p2.get(x,y));
      z = max(250.0-b,0);
      r = z/ystep*ymult;
      a += z/128.0;
      liner.vertex(x,y+sin(a)*r);
    }
    liner.endShape();
    s.addChild(liner);
  }
    
  background(255);
  s.scale(1.0/imageScaleUp);
  shape(s,isRecording ? 0 : 150,0);
}

void sldLines(int value) {
  ystep = value;
  needsReload = false;
  redrawImage();
}

void sldAmplitude(int value) {
  ymult = value;
  needsReload = false;
  redrawImage();
}

void sldXSpacing(int value) {
  xstep = 31-value;
  needsReload = false;
  redrawImage();
}

void tglInvert(boolean value) {
  invert = value;
  needsReload = true;
  redrawImage();
}

void bangSave() {
  isRecording = true;
  isRunning = true;
  redraw();
}

void redrawImage() {
  isRunning = true;
  isRecording = false;
}

void keyPressed() {
  if (key == ' ') {
    // nothing here
  } else if (key == 's') {
    isRecording = true;
    isRunning = true;
    redraw();
  }
}

SVG File of the cat -- http://broadcast.artificialcolors.com/squiggleImage_12023.svg

Now a real git repo! https://github.com/gwygonik/SquiggleDraw