MadModders forum asks that if you attach a photo, it be no wider than 800 pixels. This helps readability on most computer screens, by eliminating the sideways scroll bar. It also saves forum storage space and allows pages to load faster.
What are pixels? Well just the dots on your screen that make up an image. Pixels sizes are not the same thing as file sizes. It is possible to have a small file size, like a 40 kB photo and yet be an image that is greater than 800 pixels wide. Or a 40 kB image could be 200 pixels wide.
So what we want to do with large photos is shrink them by specifying their finished width in pixels, and not worry too much about what the final file size is.
To shrink an image to fit the forum you can use just about any photo editor, either natively on your computer or phone, or online through a number of websites. I'm going to provide here an example of using MTPaint, a very simple free photo editor, that I have loaded on my Linux computer (it's available for other OSs as well). But the steps to shrink your photo will be similar on just about any other photo editor. (Note: you can also use an online photo resizer -- see post #5 below).
With any photo, I first load it into MTPaint, and then click on the top toolbar
Image and then select
Scale Canvas from the dropdown menu, like so: