I can't figure out how to pull the target record, plus the one before and after it in a single SQL query. I suppose that can't be done.

It can be done, though it's not particularly efficient, and the exact syntax of the query will depend on which database you're using. The strategy is to outer join the table to itself twice (once for the prev, once for the next). Something like (in Oracle):

 select max(P.img_id), T.img_id, min(N.img_id)
 from images T, images P, images N
 where P.img_id(+) < T.img_id and P.uid(+) = T.uid and P.album_id(+) =
+ T.album_id
   and N.img_id(+) > T.img_id and N.uid(+) = T.uid and N.album_id(+) =
+ T.album_id
   and T.img_id = ? and T.uid = ? and T.album_id = ?
 group by T.img_id
[download]

That said, grabbing the array is a better way to do it.
Update: added other outer-joined columns.

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We're not really tightening our belts, it just feels that way because we're getting fatter.

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