It displays an image with alpha

VariableAlphaImage.ino

// include the library code:
#include <LiquidCrystal.h>

// initialize the library with the numbers of the interface pins
LiquidCrystal lcd(12, 11, 5, 4, 3, 2);

// make some custom characters:

byte BlankTopLeft[8] = {
0b00000,
0b00000,
0b00010,
0b00111,
0b01111,
0b00111,
0b00111,
0b00011
};


byte BlankTopRight[8] = {
0b00000,
0b00000,
0b00000,
0b10000,
0b11100,
0b11110,
0b11110,
0b11100
};


byte BlankBottomLeft[8] = {
0b00000,
0b01000,
0b01000,
0b00010,
0b00000,
0b00100,
0b00100,
0b00000
};

byte BlankBottomRight[8] = {
0b00000,
0b01000,
0b01000,
0b00010,
0b00000,
0b00100,
0b00100,
0b00000
};

byte TopLeft[8] = {
0b00000,
0b00000,
0b00000,
0b00001,
0b00111,
0b00111,
0b00111,
0b00011
};

byte TopRight[8] = {
0b00000,
0b00000,
0b00000,
0b10000,
0b11100,
0b11110,
0b11110,
0b11100
};

byte BottomLeft[8] = {
0b00000,
0b00100,
0b00100,
0b00001,
0b00001,
0b01000,
0b00010,
0b00010
};

byte BottomRight[8] = {
0b00000,
0b00100,
0b00100,
0b00001,
0b00001,
0b01000,
0b00010,
0b00010
};

void setup() {
  lcd.begin(16, 2);

  lcd.createChar(0, TopLeft);
  lcd.createChar(1, TopRight);
  lcd.createChar(2, BottomLeft);
  lcd.createChar(3, BottomRight);
  lcd.createChar(4, BlankTopLeft);
  lcd.createChar(5, BlankTopRight);
  lcd.createChar(6, BlankBottomLeft);
  lcd.createChar(7, BlankBottomRight);

  lcd.clear();

  lcd.print("    El tiempo");
  lcd.setCursor(0, 1);
  lcd.print("      Lluvia");
}

inline void executionDependentDelay(unsigned long* lastTime, unsigned long millisecs) {
  if(*lastTime == 0) {
    *lastTime = millis();
    return;
  }

  unsigned long timeElapsed = millis() - *lastTime;
  long diff = -((long) timeElapsed) + millisecs;
  delay(max(0, diff));
  *lastTime = millis();
}

const unsigned long TimedDelay = 15;

inline void displayAlphaChar(int charCodeNormal, int charCodeAlpha, int col, int row) {
  static unsigned long lastTime = 0;

  noInterrupts();
  lcd.setCursor(col, row);
  lcd.write(byte(charCodeAlpha));
  interrupts();
  executionDependentDelay(&lastTime, TimedDelay);
  noInterrupts();
  lcd.setCursor(col, row);
  lcd.write(byte(charCodeNormal));
  interrupts();
}

void loop() {
  displayAlphaChar(0, 4, 0, 0);
  displayAlphaChar(1, 5, 1, 0);
  displayAlphaChar(2, 6, 0, 1);
  displayAlphaChar(3, 7, 1, 1);
}