RenderImages from local file with associated checkboxes

I am very new to shiny and trying to create an app where multiple users can contribute to data collection. Its quite complicated as I first need images to load from a local folder which users analyse and check boxes to mark certain features of the photograph. The filename of each photograph matches to a dataset with data in another column that I would like to use to populate checkboxes (which will be different for each photographt) so I need the two to talk to eachother. The user sees the photo and the corresponding checkboxes, ticks certain boxes and then the data gets output to an excel file and the user clicks a "Next" action button to move to the next photograph.

So far, I have managed to load the photograph from the local folder with a next button but have no idea how to proceed - is anyone able to provide advice please? My code is as follows:

dir <- "custom.file.path"
img_files <- list.files(dir, = TRUE)

ui <- fluidPage(
        actionButton("next_btn", label = "Next"),
    plotOutput("plot", height=100)

server <- function(input, output, session) {
  output$plot <- renderImage({
    list(src = sample(img_files, 1))
  }, deleteFile = FALSE)

shinyApp(ui, server)