LinuxQuestions.org - Reduce Jpeg File Size

I normally use 'convert' from the Imagemagick package from the command line. You might look at 'Gimp.'
This is from an ai - Gemini: "
GIMP offers two main ways to reduce the file size of a JPEG image:

1. Using the Export Options:

Open your image in GIMP.
Go to File > Export As (or press Shift + Ctrl + E).
In the Export Image dialog box, under the Select File Type section, choose JPEG from the dropdown menu.
Locate the Quality slider. This controls the level of compression applied to the image. Lower quality means smaller file size but also introduces more noticeable artifacts.
(Optional) Explore Advanced Options: Click on the More Options button to access additional settings like Chroma subsampling (further reducing file size but potentially affecting color accuracy).
Preview and Adjust:
Enable the Show preview in image window checkbox to see how the image quality changes with the Quality slider.
Adjust the slider until you find a balance between acceptable image quality and desired file size.
Click Export to save your image with the chosen settings.
2. Scaling the Image:

Open your image in GIMP.
Go to Image > Scale Image (or press Ctrl + Alt + I).
In the Scale Image dialog box, adjust the Width and/or Height values to reduce the image dimensions. Lower dimensions generally lead to smaller file sizes.
(Optional) Choose Interpolation: Select an appropriate interpolation method (e.g., Lanczos for smooth scaling) from the Interpolation dropdown menu.
Click Scale to apply the changes.
Follow steps 2-7 from the "Using the Export Options" section above to save the scaled image as a JPEG with additional compression if needed.
Remember, reducing image quality through compression can introduce artifacts and loss of detail. Always find the right balance between file size and acceptable visual quality based on your specific needs."