Little Joomla module improvement

Hello, I want to do a little modification to my Joomla module. I think it's very simple for an expert, but I (A still learning Joomla developer) can't achieve it. The module is attached below. Basically, it shows Joomla articles with a thumbnail, created from the image found inside the article. You can view this 2 minutes demo video: [login to view URL] or visit the website: [login to view URL] to know more details. The problem is that the images inside the articles must be, literally, inside the article's text, inserted by you through the text editor. But if you put an Intro image or Fulltext image through the "Images and links" tab (See attached "[login to view URL]"), my module doesn't take those images to generate the thumbnails. So, if there is a image inside the article inserted through the text editor, an Intro image inserted through the Images tab and a Fulltext image also inserted through the Images tab, the priority order to select the image which will be thumbnailed should be: 1. Intro image 2. Fulltext image 3. Image inside text. So if there is no Intro image, it will find the Fulltext image, and if there isn't one, it would find the images inside the article's text. My total budget is 10$ USD. Please, to ensure that you have read my project and you have understood it and my budget, leave a message saying something like "All read". Thank you very much and best regards. PS: In attached "Possible [login to view URL]" I explain in which parts of the source code I think can be the problem.