I still don't know what exactly went wrong, but after I removed all of the OpenCV stuff and re-installed a fresh v4.1, it worked. So even though I checked all lib-files, there must have been something wrong with the linked libs (Pointing to different versions?! Links not working?!, etc.) Thanks @SGaist, your answer made me remove everthing and try the OCV version that is provided by Ubuntu 18.04. I got 3.X.X from there... After I removed this version again (because I want a newer one) and installed 4.1 from OCV page, it worked :-)

@Opa114 Thanks for the feedback. So please mark this topic as SOLVED now.

@JonB I think i won't be able to understand something more detailled and that answer the whole questions =) Thanks a lot, you ma real expert ! ;D

@Vagabond please don't forget to mark your post as solved... thanks.

@ZeBe Does the open-source licensing allow packaging a dynamically linked application and the required Qt libraries inside a single-file container Yes, as far as I understand it, but I'm no lawyer.

Hello' Again, I've decided to try it over MinGW compiler and a static build, apparently it got better but still have some errors. Here is my .pro file: QT += core gui widgets TARGET = Launcher TEMPLATE = app SOURCES += main.cpp mainwindow.cpp HEADERS += mainwindow.h FORMS += mainwindow.ui DEFINES += CURL_STATICLIB LIBS += -L"C:/Users/Banzai/Desktop/C++/QtPgrm/Mingw Real/includes/curl" -lcurl LIBS += "C:/Users/Banzai/Desktop/C++/QtPgrm/Mingw Real/includes/curl/libcurl.a" LIBS += "C:/Users/Banzai/Desktop/C++/QtPgrm/Mingw Real/includes/curl/libcurldll.a" INCLUDEPATH += "C:/Users/Banzai/Desktop/C++/QtPgrm/Mingw Real/includes" Also '#define CURL_STATICLIB' is declared in the header before the include of cURL. Here is the error I got: error: undefined reference to `curl_easy_init'. Not too sure what it could be. (I am using the 64 bits version while the compiler is 32 bits). When I've been using the 32 bits version, here is what I got: undefined reference to {WSAStartup@8,WSACleanup@0} <path>/curl/libcurl.a(easy.o): bad reloc address 0x0 in section `.data'. Apparently I've ready somewhere that I had to include something with -lwsock32, which I did this way: LIBS += -lwsock32 Unfortunately it did not seem to change anything. Thank you for your help.

Thank you. I'll be subclassing text/combo/check boxes as well.

You're welcome ! Since you have it working now, please update the thread title prepending [solved] so other forum users may know a solution has been found :) Up voting the answers that helped you will also allow other users to more easily find them.

I finally made it, thanks to your link. I was indeed using the wrong library. I also missed the libxcb plugin but I added it to the project "package" and it now works fine. I was ready to bang my head against the walls.