Then said he unto me, Son of man, lift up thine eyes now the way toward the north. So I lifted up mine eyes the way toward the north, and behold northward at the gate of the altar this image of jealousy in the entry.
The image of jealousy was an idol that Ahaz had placed in the north gate of the temple. Some believe it to have been an idol to Baal from Damascus.
Barnes' Notes on the Bible re: Ezek. 8:5,
"The glory of the Lord having departed from His seat between the cherubims in the holy of holies (see Ezekiel 9:3) rests in the threshold of the temple, to execute vengeance before it quits the house altogether Ezekiel 10:18. The "there" in the inner court, which was "full of the brightness of the Lord'S glory" Ezekiel 10:4, and at the gate of which Ezekiel stands." Source: here.
This eighth chapter begins a new stage of Ezekiel's prophecies and continues to the end of the eleventh chapter. The connected visions at Eze 3:12-7:27 comprehended Judah and Israel; but the visions (Eze 8:1-11:25) refer immediately to Jerusalem and the remnant of Judah under Zedekiah, as distinguished from the Babylonian exiles." Source: here.
Same source on Ezek. 8:3,
"door of the inner gate—facing the north, the direction in which he came from Chebar, called the "altar-gate" (Eze 8:5); it opened into the inner court, wherein stood the altar of burnt offering; the inner court (1Ki 6:36) was that of the priests; the outer court (Eze 10:5), that of the people, where they assembled.
seat—the pedestal of the image.
image of jealousy—Astarte, or Asheera (as the Hebrew for "grove" ought to be translated, 2Ki 21:3, 7; 23:4, 7), set up by Manasseh as a rival to Jehovah in His temple, and arresting the attention of all worshippers as they entered; it was the Syrian Venus, worshipped with licentious rites; the "queen of heaven," wife of Ph�nician Baal. Havernick thinks all the scenes of idolatry in the chapter are successive portions of the festival held in honor of Tammuz or Adonis (Eze 8:14). Probably, however, the scenes are separate proofs of Jewish idolatry, rather than restricted to one idol.
provoketh to jealousy—calleth for a visitation in wrath of the "jealous God," who will not give His honor to another (compare the second commandment, Ex 20:5). Jerome refers this verse to a statue of Baal, which Josiah had overthrown and his successors had replaced."
And further on vs. 5:
" gate of … altar—the principal avenue to the altar of burnt offering; as to the northern position, see 2Ki 16:14. Ahaz had removed the brazen altar from the front of the Lord's house to the north of the altar which he had himself erected. The locality of the idol before God's own altar enhances the heinousness of the sin."
Whereas, the abomination of desolation, of which Jesus told His disciples, was the Roman army which laid siege to Jerusalem in A.D. 70. The word "desolation" was used in the OT to indicate complete destruction and waste of a city or nation. See Ex. 23:29; Lev. 26:33; 2 Kings 19:25; Job 30:3; Isa. 1:7, etc.
The abomination was what caused the desolation of Jerusalem, and is referenced specifically in Luke 21:20,
" And when ye shall see Jerusalem compassed with armies, then know that the desolation thereof is nigh."
And, since Jesus referred in Matt. 24:15 to the abomination spoken of by Daniel then we can know that Daniel's prophesy was of the destruction of Jerusalem in 70 A.D. We look back at Daniel 9:24,
" Seventy weeks are determined upon thy people and upon thy holy city,..." (KJV)
Daniel's people and Daniel's city... "thy holy city"... were the Jews and Jerusalem. The prophesy was only about the Jews and Jerusalem, and their complete desolation. Daniel had thought he was asking about the end of the 70 years of desolation of their exile in Babylon, and their return to rebuild the temple in Jerusalem. He wanted to know when their exile would be over.
Gabriel was providing the full answer to Daniel's question about the end of the desolation of Israel. Not just 70 years, but 70 times seven, or 490 years.