Hi there,
That’s possible but would require a few steps and some custom CSS.
The first step would be for you to upload the image you wish to use to your Media Library. You can do that by following the steps here:
https://en.support.wordpress.com/media/
Next, you’d need to add a snippet similar to the following to the CSS panel of the WordPress.com Customizer:
.home #post-13 img {
visibility: hidden;
}
.home #post-13 .post-thumbnail {
background-image: url(https://example.png);
background-size: cover;
}
You’d need to replace two parts in the above snippet:
1. #post-13 would be replaced with the ID of the post you’re adding an image to. You can find the ID of your post by navigating to its editor and looking at the URL. For example, the post’s ID in the following screenshot is 5245:

2. https://example.png would be replaced with the URL to the image you wish to use.
As an extra note: I noticed that your site is hosted over at WordPress.com while this forum is intended for folk who are hosted elsewhere and running on the free software available here at www.ads-software.com.
The difference between the two types of WordPress (WordPress.com and www.ads-software.com) is an understandable and common point of confusion. If you’re unsure of the differences, then this guide gives a good overview.
As you’re on a paid plan over at WordPress.com, the contact form is the best place for you to access private live chat support:
https://wordpress.com/help/contact
For help with CSS questions, please post to our dedicated CSS forum:
https://en.forums.wordpress.com/forum/css-customization
Hope that helps out!