Investigating a reaction that is inconspicuously weak, slow, or coexists with other fast reactions is interesting since that can supply a capability to find new reactions or explore indecisive mechanisms, but the strategies for the investigations are still greatly limited. Herein, we apply the strategy of "finding from the data" to discuss inconspicuous reactions through improving the confidence level of detected signals. In dark-field microscopy (DFM) imaging analysis, plasmonic nanoprobes, such as silver nanoparticles (AgNPs), have been applied at a single nanoparticle level with high sensitivity, but correspondingly, the deviations caused by instrumental and operational errors are inevitable. Thus, silver shell-isolated nanoparticles (AgSHINs) as an internal reference (IR) are introduced to calibrate the scattering signals of AgNPs probe during the reactions. Two calibration factors, α and β, are used to calibrate the plasmonic scattering intensity and RGB values of the AgNPs probe of the DFM images, respectively, making the confidence level of the DFM imaging analysis greatly improved and, thus, supplying a possibility to monitor inconspicuously weak or slow reactions. As a proof of concept, the inconspicuous amalgamation of AgNP probes bathed in dilute solution of mercury higher than 1.0 × 10 mol/L was successfully monitored. In the same way, we identified the very weak oxidation process of AgNP probes by dissolved oxygen in water. These successful monitorings of inconspicuous weak or slow reactions, which might be possible to be regarded as detection deviations mistakenly, show that the use of AgSHINs as an IR can provide a precise method to discern or discover inconspicuous slow reactions in nature through the DFM imaging analysis.