When add one face tag in mainview/albums/one pictures view digikam and/or opencv fullfill the memory

Reproducible: Always

Steps to Reproduce:
1.Go to album view, switch to one picture view by clicking on thumb
2.Activate face tag to show face tag
3.Add a tag (draw it) and add a know face tag (know in recognition.db)
4. doing nothing else and wait
Actual Results:  
Digikam process use more and more memory, then opencv give and insufficient memory error message.

Expected Results:  
Face tag is added to picture without fullfill the memory and make the system unusable (have to wait for  task is finished) or all system crash.

LOGS from GDB (not a complete system crash) :
##START OF LOG ###
digikam(26113)/digikam (core) Digikam::FaceUtils::identityForTag: Found kface identity 8 for tag 38
[New Thread 0x9d1c2b40 (LWP 26192)]
digikam(26113)/KFACE KFaceIface::trainIdentityBatch: Training 1 images for identity 8
############[Thread 0x9d1c2b40 (LWP 26192) exited]
[Thread 0x94592b40 (LWP 26187) exited]
#######TAG ONE ######### 3 lignes aboveOpenCV Error: Insufficient memory (Failed to allocate 262144 bytes) in OutOfMemoryError, file /home/eric/opencv-2-4-5-SH/OpenCV/opencv-2.4.5/modules/core/src/alloc.cpp, line 52
digikam(26113)/KFACE: cv::Exception training LBPH: /home/eric/opencv-2-4-5-SH/OpenCV/opencv-2.4.5/modules/core/src/alloc.cpp:52: error: (-4) Failed to allocate 262144 bytes in function OutOfMemoryError
 
digikam(26113)/digikam (core) Digikam::FacePipeline::Private::checkFinished: Check for finish:  0 packages, 0 infos to filter, hasFinished() true
[Thread 0x95594b40 (LWP 26188) exited]
[Thread 0x93d91b40 (LWP 26189) exited]
[New Thread 0x93d91b40 (LWP 26252)]
[Thread 0x93d91b40 (LWP 26252) exited]
### End of log ###