At first I thought put a full post above column on my homepage MCCQ model, but I did not realize that if my post had more photos and a long text, it would not look nice on the homepage.

So I opted for a post above the columns, which is an excerpt of the full-post, and the image is an featured image , I want this and only this image is as large as a picture whole article (600 x 400 px)

how can I change the size of that thumbnail in the css code or changing the "src" in the html?

I tried to change the size of that thumbnail, in css, but the quality was very bad, because it was just a thumbnail resized ...

The easiest way to handle this is to make a manual excerpt in the post. A manual excerpt will always take precedence over an automatic excerpt and you can put an image in the manual excerpt the size you want. You may still have to add some CSS to hide the featured image for that post though.

How can i make an manual excerpt in the post ? with the "<!--more-->" ?

Because j'ai essayé mais cela ne marche pas ...

when you edit a post there is a section labeled 'Excerpt' - if you don't see that, click on the tab 'Screen Options' at the top right of the window and in the 'Show on screen' check off the 'Excerpt' box. Now you can enter a manual excerpt

Yes, I have this "Excerpt" area in the edit menu post, but what I dont understand is how do I choose an image that would have a larger size that "featured image" to a that automatically appears, from the "Excerpt" zone?

I tried to enter the url of my image in extract zone, and if I do that, I have a big image and a featured picture on my homepage, you say that I hide the featured image on my homepage with css code, but against on my pages "archives" and "categories", I also featured image and the big picture ... i dont know what to do

I think the easiest way would be to show my full article above the colomns and find a way to make functional "more tag" on the homepage MCCQ ... What do you think?

rectification my homepage is a "static" page

what I dont understand is how do I choose an image that would have a larger size that "featured image" to a that automatically appears

you add an <img…> html statement in and define the size - if you go to the media library and select the image and size, it should give you the url to use.

I tried to enter the url of my image in extract zone, and if I do that, I have a big image and a featured picture on my homepage, you say that I hide the featured image on my homepage with css code, but against on my pages "archives" and "categories", I also featured image and the big picture ... i dont know what to do

you use 'body.someclassname' as part of the CSS selector to targer it to only that page

I think the easiest way would be to show my full article above the colomns and find a way to make functional "more tag" on the homepage MCCQ ... What do you think?

it doesn't matter what I think, it's what you think - it's your site.

OK, I try to follow your advice, and I was able to hide the featured image on the home page in the first post with this code

td#mccq-header img.attachment-post-thumbnail{
display: none;

Now, I am trying to put in the css code for the big picture of the Excerpt appears only on the home page and not in the categories pages, but I do not know how works "body.someclassname " I can't build the code, I searched on google but i didn't find...

tell me you didn't use 'someclassname'.

'someclassname ' or some class name is where you put the class name you need to use based on the page you are dealing with. You have to look at the source of the page and find the <body….> statement.

Well ! your last answer made ​​me think a lot, and finally I managed to find the last CSS code that I was missing, but I have not managed to find a code that forces my "full-size image" to display only on the homepage, so instead I found a code which prevents the full-size image to view Category-pages ...

Here is the code:

body.archive img.aligncenter{
display: none;