GIF or JPG?
If you are interested to know what is trendy these days (or years!), have a look at Google Trends. It is easy to use and give you a good idea about information people are looking for on the web (or at least on Google).
Here is Google definition of this functionality: “Google Trends analyzes a portion of Google web searches to compute how many searches have been done for the terms you enter relative to the total number of searches done on Google over time.“
For example, you can try to see which format of images, between GIF and JPG, is most searched on Google. Results are shown in the figure below (GIF is blue and JPG red):
We can clearly see that JPG pictures are less used than GIF ones. This is normal to a certain extend, since GIF format has been made for the web. What is more interesting is that searches on JPG decrease (!)