If you're not engaged in business then you don't need a business license. What does it mean to "engage in business?" That depends on your state's labor law. If you operate a website from which you do not sell anything but, nonetheless, you derive income -- say be letting ads be published on your site -- then you're likely engaged in business.
In addition to figuring out whether you're engaged in business, you need to speak with a Florida-licensed intellectual property attorney about how to set up your "photo sharing website" properly so as to protect you from copyright infringement lawsuits, defamation lawsuits, potential charges for distributing pornography and a whole host of other readily anticipated risks. Good luck.
The above response is general information ONLY and is not legal advice, does not form an attorney-client relationship, and should NOT be relied upon to take or refrain from taking any action. I am not your attorney. You should seek the advice of competent counsel before taking any action related to your inquiry.
You should see a Florida-licensed attorney so the attorney can go over your specific activity and determine if it would qualify as a business. You may well need to at least file a DBA [fictitious name filing] if this website is operated as a business under a different name than your own. My guess is you plan to fund this site by advertising and that will make it a business, and if so it is likely a Florida business and you likely will need advice from a Florida attorney.
I am not your lawyer and you are not my client. Free advice here is without recourse and any reliance thereupon is at your sole risk. This is done without compensation as a free public service. I am licensed in IL, MO, TX and I am a Reg. Pat. Atty. so advice in any other jurisdiction is strictly general advice and should be confirmed with an attorney licensed in that jurisdiction.
Although your business may not need a license you probably should contact a local business attorney. Although many people think attorneys just add costs; we often can add value by preventing problems by reviewing contracts, labor issues, etc. I do not believe you will need a local license as it sound like your business is online. However, if you have a physical location you may need one. Talk to a local attorney - it should be worth the cost if nothing else for the peace of mind. Good luck! As a side note I am confused as to what type of business has no sales - how do you make money?