How to programatically create a post with an image

Hi, I’m trying to customize a WP for the first time and before starting to do stuff in the wrong way, I thought I better ask ??

I need to create a new post consisting of mostly only an image but not from the admin interface. I need to do my custom form to upload and image and create a post with it.

What would be the best way to do that? Should I manipulate the DB directly or are there any functions I can use to ease the work and avoid bypassing any WP mechanisms?

Thanks in advance!