image icons do not match the images they point to

Am having a slight problem and need some help. Everytime i go and have a look at a specific set of image icons in thumbnails or filmstrip the icons appear wrong as the images they display are not actually the images that are contained within the file. eg an icon showing a keyboard shows a person. if anybody has experienced this problem before let me know and also if you managed to fix it how this was achieved. i am totally over my head with this.