Converting png images to jpg is extremely simple using linux. The examples below will show you how to install ImageMagick, which is the software that actually does the conversion, and what commands to run to actually do the conversion.
The installation process outlined below is specific for Ubuntu / systems that use the apt package manager. If you are using a different distribution, you will have to install ImageMagick using the relevent package manager. Once ImageMagick is installed, the ‘convert’ command will work on other distributions perfectly fine.
$ sudo apt -y install imagemagick
Convert a png image to jpg
To simply convert a png image, to a jpg image, use the following command:
$ convert image.png image.jpg
Similar commands can be used to convert between other formats.
See the convert help listing for more options
$ convert --help
For more info on ImageMagick, check out their website at https://imagemagick.org/