@SGaist That was my problem. I compiled the libraries with MinGW 32 while my Qt's is MinGW 64. I changed the compiler and the problem is solved. Thanks for the help.

@Antonio-Ortiz I am glad to see that you could solve your problem. The wildcard option is quite helpful, but also quite dangerous, if you are not very careful.

Hi and welcome to devnet, You don't link to dlls but to lib files but you don't use the file extension. So essentially: LIBS += -lgsl -lgslcblas

Finally I used a similar library in server side. pHash library wasn't compatible with Qt5