diff --git a/Sources/App/Cap.swift b/Sources/App/Cap.swift
index 67006f6..f1e7141 100644
--- a/Sources/App/Cap.swift
+++ b/Sources/App/Cap.swift
@@ -10,9 +10,6 @@ struct Cap: Codable {
 
     var mainImage: Int
 
-    /// The version of the first classifier trained on this cap
-    var classifierVersion: Int?
-
     var color: Color?
 
     enum CodingKeys: String, CodingKey {
@@ -20,7 +17,6 @@ struct Cap: Codable {
         case name = "n"
         case count = "c"
         case mainImage = "m"
-        case classifierVersion = "v"
         case color = "f"
     }
 
diff --git a/Sources/App/CapServer+Routes.swift b/Sources/App/CapServer+Routes.swift
index 2f3ae66..20955ba 100755
--- a/Sources/App/CapServer+Routes.swift
+++ b/Sources/App/CapServer+Routes.swift
@@ -79,7 +79,7 @@ extension CapServer {
             try authenticator.authorize(request)
             let body = try request.getStringBody(request: "/classes/:date")
 
-            self.updateTrainedClasses(content: body)
+            try self.saveTrainedClasses(content: body)
             self.removeAllEntriesInImageChangeList(before: date)
         }
 
diff --git a/Sources/App/CapServer.swift b/Sources/App/CapServer.swift
index 92f2b8d..e94f883 100644
--- a/Sources/App/CapServer.swift
+++ b/Sources/App/CapServer.swift
@@ -23,6 +23,8 @@ final class CapServer {
     
     private let classifierFile: URL
     
+    private let classifierClassesFile: URL
+    
     private let changedImagesFile: URL
     
     private let fm = FileManager.default
@@ -87,6 +89,7 @@ final class CapServer {
         self.htmlFile = folder.appendingPathComponent("count.html")
         self.classifierVersionFile = folder.appendingPathComponent("classifier.version")
         self.classifierFile = folder.appendingPathComponent("classifier.mlmodel")
+        self.classifierClassesFile = folder.appendingPathComponent("classifier.classes")
         self.changedImagesFile = folder.appendingPathComponent("changes.txt")
         self.changedImageEntryDateFormatter = DateFormatter()
         changedImageEntryDateFormatter.dateFormat = "yy-MM-dd-HH-mm-ss"
@@ -465,7 +468,6 @@ final class CapServer {
         }
         var cap = cap
         cap.count = 0
-        cap.classifierVersion = nil
         caps[cap.id] = cap
         saveCapCountHTML()
         updateGridCapCount()
@@ -537,18 +539,33 @@ final class CapServer {
     
     // MARK: Classifier
     
-    func updateTrainedClasses(content: String) {
-        let trainedCaps = content
-            .components(separatedBy: "\n")
-            .compactMap(Int.init)
-        let version = classifierVersion
-        for cap in trainedCaps {
-            // Set current classifier
-            if caps[cap]?.classifierVersion == nil {
-                caps[cap]?.classifierVersion = version
+    func saveTrainedClasses(content: String) throws {
+        let classes = content.components(separatedBy: ",")
+        
+        // Validate input
+        try classes.forEach { s in
+            guard let id = Int(s) else {
+                log("Invalid id '\(s)' in uploaded id list")
+                throw Abort(.badRequest)
+            }
+            guard caps[id] != nil else {
+                log("Unknown id '\(id)' in uploaded id list")
+                throw Abort(.badRequest)
             }
         }
-        log("Updated \(trainedCaps.count) classifier classes")
+        
+        guard let data = content.data(using: .utf8) else {
+            log("Failed to get classes data for writing")
+            throw Abort(.internalServerError)
+        }
+        
+        do {
+            try data.write(to: classifierClassesFile)
+            log("Updated \(classes.count) classifier classes")
+        } catch {
+            log("Failed to write classifier classes: \(error)")
+            throw Abort(.internalServerError)
+        }
     }
     
     func save(classifier: Data, version: Int) throws {
diff --git a/Training/train.swift b/Training/train.swift
index 8398ea0..8241d1e 100644
--- a/Training/train.swift
+++ b/Training/train.swift
@@ -156,6 +156,12 @@ final class ClassifierCreator {
         }
         let changedMainImages = changedImageList.filter { $0.image == 0 }.map { $0.cap }
         let classes = imageCounts.keys.sorted()
+        
+        // Delete any image folders not present as caps
+        guard deleteUnnecessaryImageFolders(caps: classes) else {
+            return nil
+        }
+        
         return (classes, missingImageList.count + changedImageList.count, changedMainImages)
     }
     
@@ -176,6 +182,33 @@ final class ClassifierCreator {
         }
     }
     
+    private func deleteUnnecessaryImageFolders(caps: [Int]) -> Bool {
+        let validNames = caps.map { String(format: "%04d", $0) }
+        let folders: [String]
+        do {
+            folders = try FileManager.default.contentsOfDirectory(atPath: imageDirectory.path)
+        } catch {
+            print("[ERROR] Failed to get list of image folders: \(error)")
+            return false
+        }
+        for folder in folders {
+            if validNames.contains(folder) {
+                continue
+            }
+            
+            // Not a valid cap folder
+            let url = imageDirectory.appendingPathComponent(folder)
+            do {
+                try FileManager.default.removeItem(at: url)
+                print("[ERROR] Removed unused image folder '\(folder)'")
+            } catch {
+                print("[ERROR] Failed to delete unused image folder \(folder): \(error)")
+                return false
+            }
+        }
+        return true
+    }
+    
     private func imageUrl(base: URL, cap: Int, image: Int) -> URL {
         base.appendingPathComponent(String(format: "%04d/%04d-%02d.jpg", cap, cap, image))
     }
@@ -329,7 +362,7 @@ final class ClassifierCreator {
         let dateString = df.string(from: lastUpdate)
         return await post(
             url: server.appendingPathComponent("classes/\(dateString)"),
-            body: classes.map(String.init).joined(separator: "\n").data(using: .utf8)!)
+            body: classes.map(String.init).joined(separator: ",").data(using: .utf8)!)
     }
     
     // MARK: Step 7: Create thumbnails