JPEG images can be created with either baseline or progressive compression. Baseline JPEG has better support among devices. Progressive method is specifically for web site images which allows large images to be displayed “progressively” as it downloads. JPEG images with 'progressive' compression type are relatively rare in GIS. In both DigiTerra Explorer version we support the baseline compression method only, so the image does not display when inserting it
with progressive compression into a map view in DigiTerra Explorer.
Solution or WorkaroundOpen the JPEG in a third-party graphics application and save to a new file or new format without the option for 'progressive' compression in 'baseline' mode.

For example in Irfanview (Options >JPG loosless operations >Check optimizing & cleaning options only) and it works perfect in DigiTerra Explorer
Download link to IrfanView:
http://www.irfanview.com 
You can also use GIMP:
http://en.wikibooks.org/wiki/GIMP/Saving_as_JPEG 
or even XnView:
http://www.xnview.com