R, 117 63 bytes
function(m)sum(colSums(as.matrix(dist(which(m==8,T)))<=2^.5)<2)
function(m,p=which(m==8,T))sum(sapply(split(p,1:nrow(p)),function(y)sum(apply(p,1,function(x)all((c(y-x)^2<2)))))==1)
R,
ngm
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