It's difficult to tell if a filter was used, particularly since the photo appears to be greatly reduced in size. If one was used, it may have been a "warming" color-conversion filter.
Some digital cameras let you control the hue which will be applied to a photo as it is taken. For example, my camera has a Color Effect menu to select "cool," "warm," "black and white," or "sepia." I can also use the white balance setting to change the hue. But remember, these affect the color of an entire photo, unlike image editing software where you can select which areas to apply changes.
Images can be warmed up using the color balance menu found in some image editing programs. In fact, some programs have actual filter effects which can be applied to digital images during editing. A knowledge of using selection tools and/or how to use layers is necessary.
Here's information about camera filters:
http://www.tiffen.com/camera_filters.htmHere's a little program that let's you apply filter effects after your photo is taken:
http://www.mediachance.com/digicam/filtersim.htmThe photo also looks like a soft-focus filter may have been used too. A soft focus, or slight blur effect, can also be done in image editing software.