Merge pull request #26486 from gursimarsingh:object_detection_engine_update

Code Fixes and changed post processing based on models.yml in Object Detection Sample #26486

## Major Changes

1. Changes to add findModel support for config file in models like yolov4, yolov4-tiny, yolov3, ssd_caffe, tiny-yolo-voc, ssd_tf and faster_rcnn_tf.
2. Added new model and config download links for ssd_caffe, as previous links were not working.
3. Switched to DNN ENGINE_CLASSIC for non-cpu convig as new engine does not support it.
4. Fixes in python sample related to yolov5 usage.

### Pull Request Readiness Checklist

See details at https://github.com/opencv/opencv/wiki/How_to_contribute#making-a-good-pull-request

- [x] I agree to contribute to the project under Apache 2 License.
- [x] To the best of my knowledge, the proposed patch is not based on a code under GPL or another license that is incompatible with OpenCV
- [x] The PR is proposed to the proper branch
- [x] There is a reference to the original bug report and related work
- [x] There is accuracy test, performance test and test data in opencv_extra repository, if applicable
      Patch to opencv_extra has the same branch name.
- [x] The feature is well documented and sample code can be built with the project CMake

samples/dnn/models.yml

@@ -89,8 +89,8 @@ yolov5l:
   width: 640
   height: 640
   rgb: true
-  classes: "object_detection_classes_yolo.txt"
-  background_label_id: 0
+  labels: "object_detection_classes_yolo.txt"
+  postprocessing: "yolov5"
   sample: "object_detection"
 
 # YOLO4 object detection family from Darknet (https://github.com/AlexeyAB/darknet)
@@ -112,6 +112,7 @@ yolov4:
   rgb: true
   labels: "object_detection_classes_yolo.txt"
   background_label_id: 0
+  postprocessing: "darknet"
   sample: "object_detection"
 
 yolov4-tiny:
@@ -130,6 +131,7 @@ yolov4-tiny:
   rgb: true
   labels: "object_detection_classes_yolo.txt"
   background_label_id: 0
+  postprocessing: "darknet"
   sample: "object_detection"
 
 yolov3:
@@ -148,6 +150,7 @@ yolov3:
   rgb: true
   labels: "object_detection_classes_yolo.txt"
   background_label_id: 0
+  postprocessing: "darknet"
   sample: "object_detection"
 
 tiny-yolo-voc:
@@ -166,14 +169,18 @@ tiny-yolo-voc:
   rgb: true
   labels: "object_detection_classes_pascal_voc.txt"
   background_label_id: 0
+  postprocessing: "darknet"
   sample: "object_detection"
 
-# Caffe implementation of SSD model from https://github.com/chuanqi305/MobileNet-SSD
+# Caffe implementation of SSD model from https://github.com/PINTO0309/MobileNet-SSD-RealSense
 ssd_caffe:
   load_info:
-    url: "https://drive.google.com/uc?export=download&id=0B3gersZ2cHIxRm5PMWRoTkdHdHc"
+    url: "https://github.com/PINTO0309/MobileNet-SSD-RealSense/raw/refs/heads/master/caffemodel/MobileNetSSD/MobileNetSSD_deploy.caffemodel"
     sha1: "994d30a8afaa9e754d17d2373b2d62a7dfbaaf7a"
   model: "MobileNetSSD_deploy.caffemodel"
+  config_load_info:
+    url: "https://github.com/PINTO0309/MobileNet-SSD-RealSense/raw/refs/heads/master/caffemodel/MobileNetSSD/MobileNetSSD_deploy.prototxt"
+    sha1: "25c8404cecdef638c2bd9ac7f3b46a8b96897deb"
   config: "MobileNetSSD_deploy.prototxt"
   mean: [127.5, 127.5, 127.5]
   scale: 0.007843
@@ -181,6 +188,7 @@ ssd_caffe:
   height: 300
   rgb: false
   labels: "object_detection_classes_pascal_voc.txt"
+  postprocessing: "ssd"
   sample: "object_detection"
 
 # TensorFlow implementation of SSD model from https://github.com/tensorflow/models/tree/master/research/object_detection
@@ -202,6 +210,7 @@ ssd_tf:
   height: 300
   rgb: true
   labels: "object_detection_classes_coco.txt"
+  postprocessing: "ssd"
   sample: "object_detection"
 
 # TensorFlow implementation of Faster-RCNN model from https://github.com/tensorflow/models/tree/master/research/object_detection
@@ -222,6 +231,7 @@ faster_rcnn_tf:
   width: 800
   height: 600
   rgb: true
+  postprocessing: "ssd"
   sample: "object_detection"
 
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