How to modify an image for free

[xairbusdriver]

Just use Preview!

Open Preview (conveniently available in every Mac, no downloading/purchasing required).
Take your image/screen capture/etc. and store it anywhere you want.

In Preview:

• Use the "Open..." to load the image.
• Use the "Tools", "Adjust size..." menu and change any of the properties available in first image.
• Use "Export..." and save in any of seven formats. I think most forums accept jpeg, but "OpenEXR" is also available.

There is no Step 4!
I generally use ~800 pixels for maximum width to prevent horizontal scrolling.
Note to file size decrease! Lower values makes up/downloading faster and uses less of Stu's server space.