Issue
Why does req=set sometimes return type="unknown"?
Solution
To learn how req=set auto detection works, see http://microsite.omniture.com/t2/help/en_US/s7/is_ir_api/index.html#is_api-http_ref-Media_Set_Requests.
Do not depend on the set auto detection in Image Serving. Each set record should have an AssetType to get predictable behavior. A set only containing images separated with commas can be various sets, which makes it is impossible to determine the type.
http://s7g1.scene7.com/is/image/TechSupportEU/111189-0039_spin?req=set
2d spinset
Returns type="unknown:"
<set n="Company/1234567_R_S001" pv="1.0" type="unknown">
3d spinset
This option still returns the type="spin:" http://mobiletest.scene7.com/is/image/Viewers/SpinSet-Sample?req=set
<set n="Viewers/SpinSet-Sample" pv="1.0" type="spin">
For instructions on specifying the type in advance, see http://s7g1.scene7.com/is/image/TechSupportEU/?req=set&imageset=111189-0039_spin;;spin
<set n="TechSupportEU" pv="1.0" type="media_set"><item iv="uHQSA0" type="spin"><set n="TechSupportEU/111189-0039_spin" type="spin"><item dx="1000" dy="1000" iv="Zchrf1"><i n="TechSupportEU/111189-0039_1_spin"/></item><item dx="1000" dy="1000" iv="gnrrm3"><i n="TechSupportEU/111189-0039_2_spin"/></item></set></item></set>