Here's my view...
O GURUMA vs HARAI GOSHI
In (right-handed) Harai Goshi your 'loin' (top part at the back of the leg) is used to sweep Ukes leg(s). In O Guruma you pivot on your left foot and spin into the technique, but not as deeply as Harai, you contact with the front of Uke's hips/thighs rather than the top part of the outside of their thigh.
UKI GOSHI vs O GOSHI
Uki Goshi is 1-hip rather than 2, i.e. you don't turn in as deeply. Also, you can do the technique by pushing Uke's hips backwards with your hips, rather than by using a full rotation.
HIZA GURUMA vs SASAE TSURIKOMI ASHI
What Rogier said!
ASHI GURUMA vs TAI OTOSHI vs YAMA ARASHI
Tai Otoshi is a hand technique, no body (or leg!) contact required. The entry for Ashi Guruma is as for O Guruma above. There has
been lots of discussion about Yama Arashi of these boards, but th consensus lies in the placement of your hands (both on Uke's right side) and the direction of the throw, more to the side rather than the front of Uke.
HIKIKOMI GAESHI vs SUMI GAESHI
Angle of Attack (I think!)
SEOI OTOSHI vs (IPPON) SEOI NAGE
Seoi Otoshi is the proper 'drop' seoinage, the body position is lower and it's often demonstrated by bending one, or both knees, quite deeply.
I think the main problem you, and countless others, have is that you are looking at snapshots and hence cannot see the buildup and completion movements of the techniques. Judo is 4-dimensional which is hard to represent in a 2-dimensional photo or drawing.
Pete Boyes.
"Whoa, careful now. These are dangerous streets for us upper-lower-middle-class types. So avoid eye contact, watch your pocketbook, and suspect everyone." - Homer Simpson.