[Plugin: TDO Mini Forms] How to upload image only for post-thumbnail ?

Hello,

I’m in trouble because i need to add images to my posts through TDO Mini Form, but i don’t need to display them inside the post.
I just want the uploaded images used for the post thumbnails (or featured images, or custom images, i don’t know the exact word) on the homepage.

Please can anyone help me to do that?
Thank you in advance