Processing Image data changes during save - image

Question

I'm trying to create a program to hide data in a image file. Data bits are hidden into last bit of every pixels blue value. First four pixels contain the length of following data bytes.
Everything works fine when I encrypt the data to image and then decrypt it without saving the image in between. However if I encrypt the data to an image and then save it and then open the file again and try to decrypt it, decryption fails since the values seem to have changed.
I wonder if there is something similar happening as with txt files where there is BOM containing byte order data prepended into the file?
The code works if I change the color c = crypted.pixels[pos + i];
to color c = original.pixels[pos + i]; in readByteAt function
and run the encrypting function first and then the decryption function.
This causes the code to run the decryption function on the just encrypted image still in program memory instead reading it from the file.
Any ideas on what causes this or how to prevent it are welcome!
here is the full (messy) code:
PImage original;
PImage crypted;
int imagesize;
boolean ready = false;
void setup() {
size(100, 100);
imagesize = width * height;
}
void draw() {
}
void encrypt()
{
original = loadImage("image.jpg");
original.loadPixels();
println("begin encrypt");
int pos = 0;
byte b[] = loadBytes("DATA.txt");
println("encrypting in image...");
int len = b.length;
println("len " + len);
writeByteAt((len >> (3*8)) & 0xFF, 0);
writeByteAt((len >> (2*8)) & 0xFF, 8);
writeByteAt((len >> (1*8)) & 0xFF, 16);
writeByteAt(len & 0xFF, 24);
pos = 32;
for (int i = 3; i < b.length; i++) {
int a = b[i] & 0xff;
print(char(a));
writeByteAt(a, pos);
pos += 8;
}
original.updatePixels();
println();
println("done");
original.save("encrypted.jpg");
}
void writeByteAt(int b, int pos)
{
println("writing " + b + " at " + pos);
for (int i = 0; i < 8; i++)
{
color c = original.pixels[pos + i];
int v = int(blue(c));
if ((b & (1 << i)) > 0)
{
v = v | 1;
} else
{
v = v & 0xFE;
}
original.pixels[pos+i] = color(red(c), green(c), v);
//original.pixels[pos+i] = color(255,255,255);
}
}
int readByteAt(int pos)
{
int b = 0;
for (int i = 0; i < 8; i++)
{
color c = crypted.pixels[pos + i];
int v = int(blue(c));
if ((v & 1) > 0)
{
b += (1 << i);
}
}
return b;
}
void decrypt()
{
crypted = loadImage("encrypted.jpg");
crypted.loadPixels();
println("begin decrypt");
int pos = 0;
PrintWriter output = createWriter("out.txt");
println("decrypting...");
int len = 0;
len += readByteAt(0) << 3*8;
len += readByteAt(8) << 2*8;
len += readByteAt(16) << 1*8;
len += readByteAt(24);
pos = 32;
if(len >= imagesize)
{
println("ERROR: DATA LENGTH OVER IMAGE SIZE");
return;
}
println(len);
while (pos < ((len+1)*8)) {
output.print(char(readByteAt(pos)));
print(char(readByteAt(pos)));
pos += 8;
}
output.flush(); // Writes the remaining data to the file
output.close();
println("\nDone");
}
void keyPressed()
{
if(key == 'e')
{
encrypt();
}
if(key == 'd')
{
decrypt();
}
}