Automatically Thumbnails Generated and Attached

Recently I had little experiment with some of image gallery plugins. Today While I was browsing old post I was totaly shocked to see that how almost all images is in mess up condition and floating out of theme. Each Image has attached thumbnail which is displaying along with original image. Though I had totally disable thumbnail function in website right from beginning.

Please help me. I am very confused. IF I do not get some solution then I guess I shall have to correct each post one by one, which is really big task.