Don't want to display Full Size Image

[radium35]

Don't want to display Full Size Image

how would I achieve this?

[Joachim Müller]

Then don't create them in the first place. Set "Create intermediate pictures" to "no", set "Max width or height for uploaded pictures/videos (pixels)" the the same value you have set for "Max width or height of an intermediate picture/video", then set "Auto resize images that are larger than max width or height" to "Yes:Everyone".
Test your new settings by uploading a new pic that has bigger dimensions than what you have set for  "Max width or height of an intermediate picture/video". If everything works as expected (i.e. there is no full-size pop-up available for that new file), use the admin tools to resize all your existing files.