As my website probably has been affected by Panda/Penguin (at least so many people have suggested to me) I have been wondering will replacing some my photographs help boost my traffic & my search engine rankings ?, or is there other things I could do along with that or instead of that ?.
I would be using larger & hopefully more interesting ones.
I wouldn’t be changing much of the actual content … though.

As my website probably has been affected by Panda/Penguin (at least so many people have suggested to me)

Ah well, it's the latest thing for "experts" to talk bollocks about!!!

I have been wondering will replacing some my photographs help boost my traffic & my search engine rankings ?,

??? No. Why would it??

Good promotion is what gets traffic to website documents not "rankings". Any referrals from search should ALWAYS be extra and above what you get for yourself. Then your conversions are not subject to the vagiaries of search engines.