TP,

Thanks for your intimate suggestions and prompt replies. The featured image above the body text has gone once I put/add your given CSS as below:
.single #primary article img,
.page #primary article img {
display:none;
}
but all the related images which have been attached to my posts are gone away (missing again). Check this image link given below:

Again, if I remove that given CSS from the Additional CSS panel, all the attached images come back again. So there’s a CSS issue or something else beyond my imagination. Kindly look at this matter asap.

Thanks!