This application is developed to help for estimating the fish length (total length, etc.) of catch in an image at a higher speed than when measuring manually. Examples of applications include taking pictures of randomly sampled fish from catch landed at fishing ports, estimating the length composition of the total catch. The composition would be applicable for stock assessment (see note). (Note) This application does not detect fish on its own therefore it is additionally needed to prepare such as a trained deep learning model and computer to perform length estimation.A rectangular object of known size such as a box with fish is used as a ruler in this app. By inputting the size of the box in advance on the application and aligning the frame of the box with the guide frame displayed on the screen when shooting, the information on the scale necessary for length estimation is embedded in the image. In addition, information on the type of fish and the location of the photo shoot can be recorded along with the scale information. Instructions to use1. Launch the application. 2. Make the following settings from the menu in the upper left corner of the screen.2-1. Tap "Shooting Location" button and put "Add" to add a shooting location. 2-2. Select the location you have added. 2-3. Select "Fish box size" button and put "Add" and enter the name, Width, and Height of the Box.2-4. Select the added toro box from the menu.2-5. Select the fish species to be photographed. 3. Align the red frame with the frame of the box and take a picture.A preprint paper using ToroCam to estimate total length of fish is available below a preprint server.https://www.biorxiv.org/content/10.1101/2023.03.12.532319v1This application was funded by the Fisheries Agency of the Ministry of Agriculture, Forestry, and Fisheries of Japan.