I work for a California university as a writer and web developer in an insect science department. My job description also includes photography (mainly of faculty and their projects), but the university does not buy me any equipment. I buy it all myself. I've purchased about $15,000 of camera equipment. I take photos of insects in my spare time, lunch hours, on weekends, holidays, etc. Aren't the photos that I take on my own time "mine?" I use them for writing projects (my own time).
You should take a little look back to your contract agreement, if there's any rule regarding that matter. But if there's none, these are the concern that you should raise on your employer:
- Any photograph taken by you using your personal camera on the purpose of fulfilling your profession should be clearly stated on a legally-bounded agreement on whose ownership of such materials it belongs. Whether the ownership of the photograph belongs to you or to the company, the point is you and your employer, with a supporting legal process, should come up with an agreement.
- Since you bought your own equipment and you shoot "on your spare time", I think it is just right that the decisions is yours on to what photograph you may want to use and that the company recognizes you as a freelance photographer and the rightful owner of the photograph materials.
- You should be also aware of the subjects you used on taking your pictures. Who owned the subject? Are you allowed to take a photo of it? If yes, are there any conditions that you should observed? If yes, what are those?
These may be complicated, but the best thing to do is to take a look on your contract, clarify your job description, as what you said you work as a developer, and since you're also working as a freelance photographer, and if there's any additional payment you should asks, all of those concerns should be clarified.
This is a legal question and the only definitive answer will be one provided by a competent attorney who is licensed to practice in your jurisdiction and who is familiar with the subtleties of applicable statutes and common law in force within that jurisdiction. The information below is of a general nature and should not be construed as legal advice for any specific question or situation.
In general, if you own the camera and other equipment used and are using them on your own time then you own the copyright to the images you produce. There are a few other considerations, however. If you are taking the photographs on your employer's property or are taking photographs of insects that are owned by your employer or that you only have access to as a result of your employment relationship then ownership of those photos may be governed by any policies of your employer that you agreed to abide by as a condition of your employment. In that case the conditions of the contract between you and your employer would likely supersede the applicable statutes or common law that would otherwise apply.