:-) ( I was trying to post a picture of my little Mason jars containing different colors of honey in response to your Ball jar t-shirt, but the pic was so huge I decided against it. )
After you post the image url, put in width="400" or whatever you want the scale to be and it will post smaller. Here's an example:
That image is about 1300 pixels wide, but is scaled down for display to 400 pixels. Here's the html code.
<img src="https://i.redd.it/bxwo7gpray931.jpg" width="400"></img>
Before end >, add width=500”> after “.