下面是你的代码的最后一部分，显示这个想法：

  $ filename ='images / 01.png'; 
 $ bgFilename ='images / background.png'; 
 $ im = imagecreatefrompng（$ filename）; 
 $ bg = imagecreatefrompng（$ bgFilename）; 
 $ out = imagecreatetruecolor（imagesx（$ im），imagesy（$ im））; 
 $ transColor = imagecolorallocatealpha（$ out，254，254，254，127）; 
 imagefill（$ out，0，0，$ transColor）; 

 for（$ x = 0; $ x< imagesx（$ im）; $ x ++）{
 for（$ y = 0; $ y< imagesy（$ im） $ y ++）{
 $ pixel = imagecolorat（$ im，$ x，$ y）; 
 $ bgPixel = imagecolorat（$ bg，$ x，$ y）; 

 $ red =（$ pixel>>> 16）& 0xFF; 
 $ green =（$ pixel>> 8）& 0xFF; 
 $ blue = $ pixel& 0xFF; 
 $ alpha =（$ pixel& 0x7F000000）>> 24; 
 $ colorHSL = RGBtoHSL（$ red，$ green，$ blue）; 

 if（（$ colorHSL [0]> = $ colorToReplace [0]  -  $ hueAbsoluteError）&&（$ colorToReplace [0] + $ hueAbsoluteError）> = $ colorHSL [0 ]））{
 //而不是替换replaceColor 
 / * $ color = HSLtoRGB（$ replacementColor [0]，$ replacementColor [1]，$ colorHSL [2] * / 
 / * $ red = $ color [0]; * / 
 / * $ green = $ color [1]; * / 
 / * $ blue = $ color [2]; * / 
 //我们只是从背景图像像素中取颜色
 $ red =（$ bgPixel>> 16）& 0xFF; 
 $ green =（$ bgPixel>> 8）& 0xFF; 
 $ blue = $ bgPixel& 0xFF; 
} 

 if（$ alpha == 127）{
 imagesetpixel（$ out，$ x，$ y，$ transColor）; 
} 
 else {
 imagesetpixel（$ out，$ x，$ y，imagecolorallocatealpha（$ out，$ red，$ green，$ blue，$ alpha） 
} 
} 
} 
 imagecolortransparent（$ out，$ transColor）; 
 imagesavealpha（$ out，TRUE）; 
 header（'Content-type：image / png'）; 
 imagepng（$ out）; 
 

结果如下所示：

I derived a perfect color replace script from http://***.com/a/32710756/1620626. I want to replace the target color with the image background. The original image is backgrounded with light green (rgb:0b255b1). I can replace it with blue but I don't have an idea how to replace with the image. Here's the script.

This is the original image.

Once I process this photo with the script. I've got this.

The script is perfectly replace the target color with the new one. Now I want to change from blue into the background. So the final idea is. This girl on the background image I chosen.

Here is the code:

<?php
//http://***.com/a/32710756/1620626
function RGBtoHSL( $r, $g, $b ) {
    $r /= 255;
    $g /= 255;
    $b /= 255;
    $max = max( $r, $g, $b );
    $min = min( $r, $g, $b );
    $l = ( $max + $min ) / 2;
    $d = $max - $min;
    if( $d == 0 ){
        $h = $s = 0;
    } else {
        $s = $d / ( 1 - abs( 2 * $l - 1 ) );
        switch( $max ){
            case $r:
                $h = 60 * fmod( ( ( $g - $b ) / $d ), 6 );
                if ($b > $g) {
                    $h += 360;
                }
                break;
            case $g:
                $h = 60 * ( ( $b - $r ) / $d + 2 );
                break;
            case $b:
                $h = 60 * ( ( $r - $g ) / $d + 4 );
                break;
        }
    }
    return array( round( $h, 2 ), round( $s, 2 ), round( $l, 2 ) );
}

function HSLtoRGB( $h, $s, $l ){
    $c = ( 1 - abs( 2 * $l - 1 ) ) * $s;
    $x = $c * ( 1 - abs( fmod( ( $h / 60 ), 2 ) - 1 ) );
    $m = $l - ( $c / 2 );
    if ( $h < 60 ) {
        $r = $c;
        $g = $x;
        $b = 0;
    } else if ( $h < 120 ) {
        $r = $x;
        $g = $c;
        $b = 0;
    } else if ( $h < 180 ) {
        $r = 0;
        $g = $c;
        $b = $x;
    } else if ( $h < 240 ) {
        $r = 0;
        $g = $x;
        $b = $c;
    } else if ( $h < 300 ) {
        $r = $x;
        $g = 0;
        $b = $c;
    } else {
        $r = $c;
        $g = 0;
        $b = $x;
    }
    $r = ( $r + $m ) * 255;
    $g = ( $g + $m ) * 255;
    $b = ( $b + $m  ) * 255;
    return array( floor( $r ), floor( $g ), floor( $b ) );
}

/* ---------------CHANGE THESE------------------- */
$colorToReplace = RGBtoHSL(0,255,1);//target color
$hueAbsoluteError = 7;//the more the clearer
$replacementColor = RGBtoHSL(0, 192, 239);//new color
/* ---------------------------------------------- */

$filename = 'images/01.png';
$im = imagecreatefrompng($filename);
$out = imagecreatetruecolor(imagesx($im), imagesy($im));
$transColor = imagecolorallocatealpha($out, 254, 254, 254, 127);
imagefill($out, 0, 0, $transColor);

for ($x = 0; $x < imagesx($im); $x++) {
    for ($y = 0; $y < imagesy($im); $y++) {
        $pixel = imagecolorat($im, $x, $y);

        $red = ($pixel >> 16) & 0xFF;
        $green = ($pixel >> 8) & 0xFF;
        $blue = $pixel & 0xFF;
        $alpha = ($pixel & 0x7F000000) >> 24;

        $colorHSL = RGBtoHSL($red, $green, $blue);

        if ((($colorHSL[0]  >= $colorToReplace[0] - $hueAbsoluteError) && ($colorToReplace[0] + $hueAbsoluteError) >= $colorHSL[0])){
            $color = HSLtoRGB($replacementColor[0], $replacementColor[1], $colorHSL[2]);
            $red = $color[0];
            $green= $color[1];
            $blue = $color[2];
        }

        if ($alpha == 127) {
            imagesetpixel($out, $x, $y, $transColor);
        }
        else {
            imagesetpixel($out, $x, $y, imagecolorallocatealpha($out, $red, $green, $blue, $alpha));
        }
    }
}
imagecolortransparent($out, $transColor);
imagesavealpha($out, TRUE);
header('Content-type: image/png');
imagepng($out);
?> 

You can just read two images, source and background, and take pixels from background image and set to the source.

Below is the last part of your code above which shows this idea:

$filename = 'images/01.png';
$bgFilename = 'images/background.png';
$im = imagecreatefrompng($filename);
$bg = imagecreatefrompng($bgFilename);
$out = imagecreatetruecolor(imagesx($im), imagesy($im));
$transColor = imagecolorallocatealpha($out, 254, 254, 254, 127);
imagefill($out, 0, 0, $transColor);

for ($x = 0; $x < imagesx($im); $x++) {
    for ($y = 0; $y < imagesy($im); $y++) {
        $pixel = imagecolorat($im, $x, $y);
        $bgPixel = imagecolorat($bg, $x, $y);

        $red = ($pixel >> 16) & 0xFF;
        $green = ($pixel >> 8) & 0xFF;
        $blue = $pixel & 0xFF;
        $alpha = ($pixel & 0x7F000000) >> 24;
        $colorHSL = RGBtoHSL($red, $green, $blue);

        if ((($colorHSL[0]  >= $colorToReplace[0] - $hueAbsoluteError) && ($colorToReplace[0] + $hueAbsoluteError) >= $colorHSL[0])){
            // Instead of taking the replacementColor
            /* $color = HSLtoRGB($replacementColor[0], $replacementColor[1], $colorHSL[2]); */
            /* $red = $color[0]; */
            /* $green= $color[1]; */
            /* $blue = $color[2]; */
            // We just take colors from the backround image pixel
            $red = ($bgPixel >> 16) & 0xFF;
            $green = ($bgPixel >> 8) & 0xFF;
            $blue = $bgPixel & 0xFF;
        }

        if ($alpha == 127) {
            imagesetpixel($out, $x, $y, $transColor);
        }
        else {
            imagesetpixel($out, $x, $y, imagecolorallocatealpha($out, $red, $green, $blue, $alpha));
        }
    }
}
imagecolortransparent($out, $transColor);
imagesavealpha($out, TRUE);
header('Content-type: image/png');
imagepng($out);

The result can look like this: