Compare and contrast the images, tone and theme of the poems "How Do I Love Thee? Let Me Count The Ways" by Elizabeth Browning and "Do Not Go Gentle into that Good Night" by Dylan Thomas.

Thematically, both poems are about love, but Browning's "How do I Love Thee?" concerns a person's romantic love for another person, while Thomas focuses on a son's love for his father. We know that that the narrator of "Do Not Go Gentle" is a son, because he says in the last stanza "and you, my father." In "How do I Love Thee?" we often assume the speaker is a woman, because the poem was written by a woman, but since no gender is given, we can understand it as a beloved of any gender addressing the loved one. 
Both poems convey deep attachment to the person addressed and each addresses the beloved person directly, but "How do I love thee?" has a gentler tone, while the tone of Thomas's poem is relentlessly fierce. In Thomas's poem, the narrator demands that his elderly father fight for his life as long as possible, repeating over and over again "do not go gentle into that good night." By "that good night," the narrator means death. The imagery that he uses is violent and raw: 

Old age should burn and rave at close of day

He repeatedly says that his father should 

Rage, rage against the dying of the light.

Words like "burn" and "rave" and "rage" are angry, high-energy words, words that make us think of getting fired up and fighting back. Thomas uses other fierce, high-energy images to further emphasize his point: He talks about "wild men," who "caught and sang the sun in flight." Wild men, of course, are fierce and active, and verbs like "caught" and "sang" are active, vital, high-energy words as well. One must be fierce too to catch something as powerful and burning as the sun. The sun "in flight" brings to mind the image of fast-paced motion. 
Thomas turns the blindness we associate with old age into fierce, bright, high-energy imagery with words like "blinding," which means bright, "blaze," which makes us think of fire, and "meteors," which shoot rapidly across the sky:

men...who see with blinding sightBlind eyes could blaze like meteors... 

He also tells his father to "Curse, bless, me now with your fierce tears, I pray."
The tone, with its repeated images of rage, fire and light, is meant to inspire his father to rally all his energy and force to fight off death.
Browning's narrator also conveys deep passion towards the beloved. The narrator communicates this by writing: "I love thee [you] to the depth and breadth and height my soul can reach." In other words, if we imagine the love stretching out in all directions, the narrator loves the beloved totally, with every ounce of strength, in an all-encompassing way. The passion is also reinforced by repetition of the phrase "I love thee" over and over: one line does not convey all the love: instead, the love has multiple dimensions.
At the same time, the poem has a gentler, quieter tone than Thomas's poem and does not use the same fierce images. Browning uses more domestic images, such as in these lines: 

I love thee to the level of every day'sMost quiet need, by sun and candlelight.

Words such as "level," "every day," "quiet," and "candlelight" are not fierce and wild but simple, gentle, and calm. The love is free and pure and the "passion put to use," as if it is channeled constructively rather than burning wildly. It is the ever-present quality of this love, always there in ordinary, everyday life, that conveys its depth.
Unlike Thomas, this narrator doesn't fight against the possibility of death or tell the beloved to fight death. Here, death is not an end, "a dying of the light." Instead, the narrator in Browning's poem believes their love will continue beyond the grave, saying: "I shall but love thee better after death."