DOCBOOK: DTD doubts

I have certain doubts regarding DTD .
> 1.Can we have two DTD's for an XML (it can be either directly or
> indirectly,like a DTD which inturn has two DTD mentioned)?
> If so how it can be done?
> 2.I have another doubt regarding DTD ,hope apart from text(PCDATA&
> CDATA) it doesnot support other datatypes so XML schema is the only
> soln. for this ,but I feel even Schema doesnot support datatype of
> Binary type(image )
> So can I get suitable soln. for declaring image type?
> 
> Pls getback to me ASAP	
> Can u provide me the URL if any site has answer for this
> 
> 
> Regards
> Sasi