Take photos . . .
Place in envelope (preferably reinforced) . . .
Add address and correct postage . . .
N.B. It may be wise to add a return address. Also note that although the Post Office accepts the post code written on the same line as the county (six character spaces between) I would advise one uses a separate line.
Drop in postbox . . .
. . . unless, of course it is too big, in which case one must make a trip to a post office . . .