jsはリッチテキスト（正規表現）で最初の画像を取得します。

var imgUrlFun = function(str){
  var data = '';
   str.replace(/<img [^>]*src=['"]([^'"]+)[^>]*>/, function (match, capture) {
     data = capture;
   });
  return data
 }

var filterHTMLTag = function (str) {
  str = str.replace(/<\/? [^>]*>/g,''); // remove HTML tag
  str = str.replace(/[ | ]*\n/g,'\n'); //remove end-of-line whitespace
  str = str.replace(/ /ig,'');// remove 
  return str;
 }

Pattern p_img = Pattern.compile("(]+src\s*=\s*'\"['\"][^>]*>)");
Matcher m_img = p_img.matcher(content);
while (m_img.find()) {
String img = m_img.group(1); //m_img.group(1) to get the whole img tag m_img.group(2) to get the value of src
}

/**
 * [getPic description]
 * Get the address of the first picture in the text
 * @param [type] $content [description]
 * @return [type] [description]
 */
 function getPic($content){
  if(preg_match_all("/(src)=([\"|']?) ([^ \"'>]+\. (gif|jpg|jpeg|bmp|png))\2/i", $content, $matches)) {
   $str=$matches[3][0];
  if (preg_match('/\/Uploads\/images/', $str)) {
   return $str1=substr($str,7);
  }
 }
}

$content=I('post.body');//Get rich text editor content
  $info=getPic($content);//use function to return matching address claim thumbnail if not empty
  if(! $info==null){
   $thumb=$info.'thumb240x160.png';
   $image = new \Think\Image();//Instantiate image processing, thumbnail function
   $image->open($info);// Generate a centered thumbnail cropped to 240*160
   $unlink=$image->thumb(240, 160,\Think\Image::IMAGE_THUMB_CENTER)->save($thumb);
  }else{
   $thumb='';
  }

function get_firstimg(){
 //var c=document.getElementById('body').value;
 var c=FCKeditorAPI.GetInstance('body').GetXHTML(true);
 if(c){
 var fimg=c.match(/<img(. *?) src=["|'](. *?) ["|'](. *?) >/);
 if(fimg[2]){
 document.getElementById('picname').value=fimg[2];
 if(document.getElementById('ImgPr'))document.getElementById('ImgPr').src=fimg[2];//preview
 if(document.getElementById('picview'))document.getElementById('picview').src=fimg[2];//preview
 }
 }
}

var content= UE.getEditor('details').getContent();//Get the editor content
var $div = document.createElement("div");//create a div element object
$div.innerHTML = content;//fill the div with html
var $v = $($div);//convert from a dom object to a jquery object
$.each($v.find("img"),function (v,i) {//selector find img element, loop to get src value
console.log("src======"+i.src);
});

<p style="margin-top: 1em; margin-bottom: 1em; white-space: normal; box-sizing: border-box; padding: 0px; border: 0px; vertical-align: middle; line-height: 25px; list-style: none; color: rgb(58, 58, 58); font-family: 微软雅黑, 宋体, Verdana, Arial, Helvetica, sans-serif; font-size: 14px; background-color: rgb(247, 253, 255);">
	Summer is here and the constant heat is too much for even adults, let alone children. So should you give your child to wear socks again became the big thing on the mind of the baby mother, on the one hand, think you should give your child to wear, after all, this several reasons can not refuse.
	</p>
	<p style="margin-top: 1em; margin-bottom: 1em; white-space: normal; box-sizing: border-box; padding: 0px; border: 0px; vertical-align: middle; line-height: 25px; list-style: none; color: rgb(58, 58, 58); font-family: 微软雅黑, 宋体, Verdana, Arial, Helvetica, sans-serif; font-size: 14px; background-color: rgb(247, 253, 255); text-align: center;">
	<img alt="1.jpg" width="490" height="306" src="http://www.socksb2b.com/d/file/zixun/wazichangshi /2019-07-05/1b0038e6cf808ae9c091c34ded031de9.jpg" _src="http://www.socksb2b.com/d/file/zixun/wazichangshi/2019-07-05/ 1b0038e6cf808ae9c091c34ded031de9.jpg">
	</p>
	<p style="margin-top: 1em; margin-bottom: 1em; white-space: normal; box-sizing: border-box; padding: 0px; border: 0px; vertical-align: middle; line-height: 25px; list-style: none; color: rgb(58, 58, 58); font-family: 微软雅黑, 宋体, Verdana, Arial, Helvetica, sans-serif; font-size: 14px; background-color: rgb(247, 253, 255);">
	There is also a part of the baby mothers who have a different opinion and think it is better to not wear socks:.
	</p>
	<p style="margin-top: 1em; margin-bottom: 1em; white-space: normal; box-sizing: border-box; padding: 0px; border: 0px; vertical-align: middle; line-height: 25px; list-style: none; color: rgb(58, 58, 58); font-family: 微软雅黑, 宋体, Verdana, Arial, Helvetica, sans-serif; font-size: 14px; background-color: rgb(247, 253, 255);">
	1. small children often sweat, metabolism is relatively fast, socks if not breathable, there is a risk that the child will be crying because of raw foot sweat.
	</p>
	<p style="margin-top: 1em; margin-bottom: 1em; white-space: normal; box-sizing: border-box; padding: 0px; border: 0px; vertical-align: middle; line-height: 25px; list-style: none; color: rgb(58, 58, 58); font-family: 微软雅黑, 宋体, Verdana, Arial, Helvetica, sans-serif; font-size: 14px; background-color: rgb(247, 253, 255);">
	2. The soles of the feet have many acupuncture points, and without socks you can fully massage the soles of the feet. Beneficial to the operation of other body functions. Relieve constipation, indigestion and other symptoms.
	</p>
	<p style="margin-top: 1em; margin-bottom: 1em; white-space: normal; box-sizing: border-box; padding: 0px; border: 0px; vertical-align: middle; line-height: 25px; list-style: none; color: rgb(58, 58, 58); font-family: 微软雅黑, 宋体, Verdana, Arial, Helvetica, sans-serif; font-size: 14px; background-color: rgb(247, 253, 255);">
	It seems like both parents have a point, so should you wear socks or not?
	</p>

var $div = document.createElement("div");//create a div element object
$div.innerHTML = content;//fill the div with html

$.each($v.find("img"),function (v,i) {
console.log("src======"+i.src);
});