String[] lines = { "I am an alien", "Will you talk with me?" }; // the lines to put onto one image
setImage(multiLineImage(lines, 30, Color.BLACK, new Color(0, 0, 0, 0))); // setting needed image to actor

private GreenfootImage multiLineImage(String[] lines, int fontSize, Color textColor, Color backgroundColor)
{
    int lineCount = lines.length; // number of lines
    GreenfootImage[] lineImages = new GreenfootImage[lineCount]; // array for images of each line
    int maxWidth = 0; // to track widest line created
    for (int i=0; i<lineCount; i++) // for each line to create
    {
        lineImages[i] = new GreenfootImage(lines[i], fontSize, textColor, backgroundColor); // create line
        if (lineImage[i].getWidth() > maxWidth) maxWidth = lineImage[i].getWidth(); // record if widest, so far
    }
    int lineHeight = lines[0].getHeight(); // height of a line
    GreenfootImage img = new GreenfootImage(maxWidth, lineCount*lineHeight); // create blank image (full-sized)
    for (int i=0; i<lineCount; i++) // for each line
    {
        img.drawImage(lines[i], 0, lineHeight*i); // draw line onto full-sized image
    }
    return img; // return full-sized image with all lines drawn onto it
}