Let me add something that I think can be added to this tutorial. Let's say we have an image like this

Yung ratio niya on the board itself is yung kung anong pixel size niya. Malaki talaga yung image kasi high quality din.
So there are two ways to resize it.
- Add letters "s,b,t,m,l,h" add the end of the File Name or the uploaded file name
- Add "width=X" or "height=y"
For the first one. This only works when you upload it in imgur.
[img]https://i.imgur.com/YIPNDO4.png[/img]
The letters s,b,t,m,l,h should be added at the end like this
[img]https://i.imgur.com/YIPNDO4s.png[/img]

[img]https://i.imgur.com/YIPNDO4l.png[/img]

Easy as that!
For the second oneI have discovered that you could just add "width" or "height", not both. Like this
[img width=300]https://i.imgur.com/YIPNDO4.png[/img]

or
[img height=200]https://i.imgur.com/YIPNDO4.png[/img]

So in summaryYou could add a letter (if you are using imgur) to determine if it would be a small square, big square, a small thumbnail, medium thumbnail, large thumbnail, and huge thumbnail. s,b,t,m,l,h respectively.
The adding of only height or width would automatically retain its aspect ratio no matter what you input. You don't need to think about whatever combination of 1024x768 or something like that. It would save us time.