Not just here and now but anytime...I tried to post a pic with postimage.org but don’t know what to to do after creating an account (I think I did that part right?)
Well, uh, upload your pic to your new account, from your computer/phone/camera, then you use the URL for the pic.
the HTML is < img src=(URL here) width=25% >
Remove the spaces between the carrots and the HTML.
I put them in so you could see what it looks like.
The % is the percent of the page you want the pic to post. 100% being the full page width.
The height will automatically adjust.
Is that what you needed?