How can i add a standard wanted image in classified
 

Is there any way a standard "wanted" image be shown in the screenshoot below instead of the "No Thumbnail" notice using photopost classified

Not unless you actually edit the templating to add imaging into that template type. The wanted template set does not use imaging.

If you want to allow images like the for sale template does then you can make copies of the editproduct.tmpl,showcat.tmpl,showproduct.tmpl and uploadproduct.tmpl templates and rename those copies accordingly appending a 1 after them so they are for example showproduct1.tmpl etc. You can then upload those templates to the proper templates folder and your wanted templates would allow images then.