Yosemite Photos: How to select only photos
To do so, you can create Smart Albums

These can be set to filter based on filetype.  You can set as many of these as you wish, and even modify existing ones.

In Photos go to File > New Smart Album or ⌘+⌥+N

Then you can set your filter criteria in several ways.  See the attached screenshot illustrating a PNG filter.



UPDATE: If you choose to use the Search field, enter just "jpg" without quotes to get a dropdown that shows filetype.