[TYPO3-dev] Adding image Size in Boostrap Package

[Christoph Heidelmann]

Hello everybody,

i am really new in Typo3 and maybe it is really easy to achieve this task.
I have Typo3 in the version 6.2. The introduction package is installed.
I want to add two properties to the image content element that set the maximum height and width of the image object.
I don't really get how to add new fields to the content element and i am also not able to change the layout of the image tag.
Can somebody help me with this please?

Thanks already!