Are the commas necessary?

The commas are necessary for the sake of clarity because the dependent clause, "to only a slight degree," is placed in the middle of the independent clause, "Life resembles the popular image of it."

The commas are necessary. However--and this is just a suggestion--if you wish to use less, or no, commas, you could rephrase your sentence. For instance, you could say: Life only slightly resembles the popular image of it.