When using someone elses work, it is common practice to give credits to the original creator. If that info is not available then one should give credits to the site which the original material is obtained.
If you are the originator of this material then you should state so with copyright statement and such. I suspect you are not originator.
I wonder if this is how you obtained most of your sites content.
You see the point, if you copy one portion of someone elses work, then all you web sites content is brought into question...