Change default max image width (600px)

You can change this property in the infamous constant editor. How? Click on Template, click on the page where the main typoscript template is located (the root page, TYPO3 Buddy in our case). Choose Constant editor in the first pull down menu. Choose the main template in the second pull down menu. Choose CONTENT in the third (category) pull down menu. Scroll down to the Image part. Look for styles.content.imgtext.maxW.

It's also possible to edit the main template directly and use the following script:

In CONSTANTS:

styles.content.imgtext.maxW = 1920

In SETUP:

tt_content.image.20.maxW = 1920

In TS Config of the Root page (for plain images not resized by Image Magick):

RTE.default.buttons.image.options {
  # realistic plain insert sizes
  plain.maxWidth = 1920
  plain.maxHeight = 1080
}