Can someone explain tweeting to me

[the*scarlet*pimpernel]

I kind of understand tweeting. What I want to know is, can I copy the photos from other peoples tweets and use them on a website or do I need to find the original tweeter and ask their permission?

[lloydslights]

I think they could be the work of Dean Sewell.  

He has contributed photos to Groundswell Gloucester.

DEB