CSS Remove very thin outline around the inserted image.

The code in the style sheet that makes it look like that is located on code line 191 to 193:

Code:

#contents img {
    border: 1px solid rgba(231, 231, 231, 0.8);
}

and code line 515 to 517:

Code:

#contents .images img.box {
    border: 5px solid #fff;
}

You remove this from your new image by using a higher rank selector to override the style for example:

Code:

#contents .images img.mynewclassname {
    border: 0px none none;
}

You can also just remove it from all images by deleting border styling from code line 191 to 193 and code lines 515 to 517.