"Say Cheese"

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I've looked for "cheese" and I think it's British. No one checks the  OED??
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(OED)
cheese 
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e. School slang. A smile. Also, esp.  Photographers' colloq., the word ‘cheese
’ notionally or actually  pronounced to form the lips into a smiling 
expression. 
1930  [see _CHEESE_ 
(http://dictionary.oed.com/cgi/crossref?query_type=word&queryword=cheese&first=1&max_to_show=10&sort_type=alpha&search_id=Gzmo-FzTJkr-64
78&result_place=1&xrefword=cheese&ps=v.&homonym_no=1)  v.1 2]. 1956  Punch 1 
Feb. 179/1 They are  almost certainly just saying cheese, cheese, cheese to 
hold their smiles  while the news reel camera whirls. 1964  New Statesman 17 
Apr. 612/3 Her  deadpan face mouths a tiny ‘Cheese’ as she is pegged..into focus.
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  2.  School slang. To smile.  
1930  N. & Q. CLVIII. 119/1  Another slang use of the word ‘cheese’ was in 
vogue at Rugby  School... This was with the meaning ‘smile’, both verb and 
noun. 1940  _M. MARPLES_ 
(http://dictionary.oed.com/help/bib/oed2-m2.html#m-marples)  Public School Slang 40  Cheese..to smile or grin (Oundle  1920+).

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