Default image width limit to 600 px in Typo3.
We can easily change this setting using TypoScript.
These TypoScript can be usually located on the root Template record.
If not you can try using the object browser to find the exact location.
Following typoscript should do the trick:
In CONSTANTS: styles.content.imgtext.maxW = 800 In SETUP: tt_content.image.20.maxW = 1080
We can also set height of image.
Like : tt_content.image.20.maxH = 500
If you have any queries, please do not hesitate to contact me at Jainish Senjaliya