Answer
$5040$ different arrangements.
Work Step by Step
"...in a row..." - order matters. Permutations.
We are taking r=7 from n=7 portraits, $P(n,r)=\displaystyle \frac{n!}{(n-r)!}$.
$ P(7,7)=\displaystyle \frac{7!}{(7-7)!}\qquad$ ... 0!=1, by definition
$P(7,7)=7!$
$=7\times 6\times 5\times 4\times 3\times 2\times 1$ = $5040$ different arrangements.