An image-based method for determining H₂O₂ vapor pressures in powder systems was developed based on cellulose pellets loaded with potassium titanium oxide oxalate (PTO Pellets) as probe particles. Solid titanyl salts change color after exposure to hydrogen peroxide vapor and the quantitative response of PTO pellets to H₂O₂ has been established by comparing reactions with H₂O₂ in liquid and solid states. Analysis of pictures of the color changes of PTO Pellets mixed into powders can be used to monitor the presence of ppm levels of H₂O₂ vapor inside powder systems such as bleach containing dry detergent powders. • H₂O₂ vapor quantification in dry systems with titanyl loaded cellulose particles. • Simple fabrication of H₂O₂ probe particles. • High sensitivity with LOD 0.190 ppm H₂O_2.