You should check the visa issuing regulations at the following web page:
http://www.mvep.hr/en/consular-information/visas/visa-requirements-overview/

Here is a part of the regulation:

“Aliens must apply for a visa prior to their entry into the Republic of Croatia, at the competent diplomatic mission/consular post. If there is no Croatian diplomatic mission/consular post in the applicant’s country, application may be submitted to the nearest Croatian diplomatic mission/consular post.

An alien shall apply for the visa personally. Exceptionally, an alien need not to file the application personally, but they shall present themselves when called upon by the diplomatic mission/consular post.”

Aliens shall enclose the following documents with the application:
– valid travel document
– the validity period of the travel document should exceed that of the visa by three months
– travel document must be issued in the previous 10 years
– travel document must contain at least two empty pages for the visa
– a 35×45 mm colour photo
– evidence of travel health insurance
– evidence of paid visa fee
– documents that prove:
– the purpose of the stay in Croatia
– ensured accommodation
– means of subsistence to cover their stay in Croatia and the return to their country of origin or to a third country
– means of transport and their intention to return to their country of origin or to a third country

Visa is entered into a foreigner’s travel document and is issued with the validation date not exceeding the document’s validation date.

In case the visa is not issued, the official person that received the application is not obliged to disclose the reasons.

You will have to appear at the nearest consular office to you in person in order to get the visa! If you are prepared to go there personally we can send you an official invitation letter (by filling out the official invitation letter form located at the Ministry of Foreign Affairs’ web site).

We can send you the invitation letter only upon:
– the approval of your application
– regulating the payment of the ADA 2014 summer school fee (if applicable). All the information are at the ADA 2014 summer school web under the category Application.

Failure to provide all of the above mentioned documentation will prevent us in issuing the letter of invitation.