In 2AD Ovid wrote the Ars Amatoria a sort of Roman dating guide. The first two books are directed at men and the third at women. While it largely deals with behaviour and where to meet potential partners there are also bits and pieces about physical appearance and how to best show off your assets.

Both men and women get tips for instance:

"A pale complexion ill becomes a sailor. The rays of the sun and the salt spray should have tanned his features; nor does it suit the husbandman who, with plough or heavy rakes, is for ever turning up the soil in the open air; and ye who strive for the athlete's crown of olive, it would ill beseem you to have too white a skin."

Or for women:

"Rare, however, is the face without a fault. Hide these blemishes with care, and so far as may be, conceal the defects of your figure. If you are short, sit down, lest when standing you should be thought to be sitting; if you are a dwarf, lie stretched at full length on your couch, and so that none may see how short you are, throw something over your feet to hide them. If you are thin, wear dresses of thick material and have a mantle hanging loosely about your shoulders. If you are sallow, put on a little rouge; if you are swarthy, see what the fish of Pharos will do for you. Let an ungainly foot be hid in a white leathern shoe. If your legs are thin, don't be seen unlacing your sandals. If your shoulder-blades are prominent, little pads will correct the defect. If you have too full a bust, contain it with a brassière. If your fingers are stumpy and your nails unsightly, don't gesticulate when you are talking. If your breath is strong, you should never talk when your stomach's empty, and always keep some distance away from your lover. A woman whose teeth are discoloured, or prominent, or uneven, will often give herself away when she laughs ... Some women cannot laugh without making a hideous grimace; others try to show how pleased they are, and you would imagine they were crying; others offend the car with harsh and ugly sounds; like the noise a dirty old she-ass makes as she brays at the mill-stone."

Ovid also speaks quite frankly about sex, with such tips as make sure your armpits smell nice, don't forget to shave your legs and

"If a woman has a lovely face, let her lie upon her back; if she prides herself upon her hips let her display them to the best advantage. Melanion bore Atalanta's legs upon his shoulders; if your legs are as beautiful as hers, put them in the same position. If you are short, let your lover be the steed."

So it would seem that the Romans certainly had plenty of ideas of what made an ideal body and ways to imitate it.

Check out Homer's description of Thersites in the second book of the Iliad. We can easily interpret that people did not want to look like this:

"He was the ugliest of all who had come to Ilium, bandy-legged and lame of foot; rounded shoulders hunched over his chest; and above them a narrow head with a scant few hairs."

On the other hand, we get to see how Hera prepares herself when she goes to seduce Zeus in the fourteenth book of the Iliad:

"She cleansed all the dirt from her fair body with ambrosia, then she anointed herself with olive oil, ambrosial, very soft, and scented specially for herself- if it were so much as shaken in the bronze-floored house of Jove, the scent pervaded the universe of heaven and earth. With this she anointed her delicate skin, and then she plaited the fair ambrosial locks that flowed in a stream of golden tresses from her immortal head. She put on the wondrous robe which Minerva had worked for her with consummate art, and had embroidered with manifold devices; she fastened it about her bosom with golden clasps, and she girded herself with a girdle that had a hundred tassels: then she fastened her earrings, three brilliant pendants that glistened most beautifully, through the pierced lobes of her ears, and threw a lovely new veil over her head. She bound her sandals on to her feet"

Some of the specifics of the Greek aren't really known, I should let you know. What stands out to me in this passage is that the form of the body itself is entirely lacking. We can boil it down to smooth, clean, perfumed skin, a nice hairdo, fancy clothes, and golden jewelry; these look like symbols of wealth more than symbols of beauty to my modern sensibilities.

Follow up to this, if no such evidence exists, around what time period do we have the earliest evidence of image issues in society?

The Romans were not concerned with ideals in their art, and portrait busts from the period demonstrate their interest in depicting people as realistically as possible. Now this is a different story with the Emperors, naturally. Even in those cases, however, they avoided idealized male nudity in favor of depictions of military power: strong, imposing, armored figures representing Rome's might. The Romans didn't do male nudity. A barbarian might traipse about half-naked in the woods, or a slave might be sold completely naked, but a citizen should always keep his body constrained. So from a male perspective, it didn't really matter what your body looked like. In fact, being overly concerned with one's body would be vanity, which was shameful for a Roman man.