Steve2018:
Is that not lifting (after searching) a request from the files on the sd card after its been sent to the webpage?
You don't send stuff to a web page. So I do not understand what you mean.
Steve2018:
Its looking for index.htm, page2.htm or pic.jpg.
You get a request for something; a html document, a css file, an image, whatever. You analyse the request and handle accordingly.
To put the example in perspective, when you visit arduino.cc, your browser sends a GET request to the server (GET https://www.arduino.cc/ if you look in the F12 window). This is a request for the root of the page as there is no filename specified; now web servers have some rules and one of them tells the webserver that if it receives a request without a filename, it should 'send' e.g. index.php (in the example that you don't understand, index.htm). You could also have requested arduino.cc/index.php which tells the browser that you want the specific page and the browser will 'send' that page.
Please note that arduino.cc uses dynamic web pages (php in this case) which will first be processed by the server to e.g. retrieve data from a database; the result of that processing is send to the browser (and hence send in the previous paragraph is between single quotes).
Now you click one of the links on that page, e.g. "buy an arduino"; the browser will now send a GET request to the server (GET https://store.arduino.cc/). This is similar (not exactly the same) to a request for your page2.htm.
Steve2018:
I am sending my webpage details to the page within my code and they work fine.
That does not mean it's the preferred / correct approach. It's far better to store your pages and pictures on sd card as it gives you the flexibility to add and modify without having to rewrite your code each time that you want to change something; simply modify the file on the sd card.
Steve2018:
I would have thought (obviously incorrectly) that there would be no difference in me directly sending the pic.jpg file like I have the rest of the webpage.
Of course there is a difference; the one is hard-coded in your code, the other one is a file.
Steve2018:
Anyway, I clearly don't understand that bit, so I will have to rethink my method.
No, you will have to understand that part. Rethinking will only help if you are not going to use images, style sheets, other pages etc.