In photography hypo is used to dissolved unaffected $AgBr$
The photographic plate is coated with the thin layer of an emulsion of silver bromide dispersed
in gelatin. Hypo or sodium thiosulphate $(Na_{2}S_{2}O_{3})$ is used in the fixing of image. It
dissolves unaffected AgBr but leaves metallic silver unchanged
$\underset{\text{Hypo}}{{2Na_{2}S_{2}O_{3}}} + AgBr \to \underset{\text{Soluble}}{{ Na_{3}\left[Ag\left(S_{2}O_{3}\right)_{2}\right]}}+NaBr$