The majority of Cuscuta photos that are posted worldwide online belong 
to only a few species: Cuscuta campestris, C. epithymum, C. europaea, C. gronovii, C. pacifica (reported as C. salina). Considering that many Cuscuta sp. are known only from their type specimens or they are very rare (or even extinct), finding photos of living plants for all the taxa listed below is an impossible job, and anyway, if you want to identify a Cuscuta spp. you must use the basic morphology galleries.
In general, I linked directly to the online source. Please make sure that you respect the rules of the website/owner of the images. I am only making sure that the identity of the taxon illustrated is correct. The list of species below is not a synopsis of the genus (I may have missed some good species).
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Various photos with Cuscuta spp. in their habitat, and sometimes the people hunting them
Alphabetical list of species
Cuscuta acuta Engelm.
Cuscuta acutiloba Engelm.
Cuscuta abyssinica Richard
Cuscuta africana Thunb.: Phytoimages
Cuscuta alata Brandegee
Cuscuta americana L.: Phytoimages; Flickr (K. Bradley)
Cuscuta andina Phil.
Cuscuta angulata Engelm.: Phytoimages
Cuscuta appendiculata Engelm.
Cuscuta approximata Bab.: Plantarium; Parasitic Plant Connection
Cuscuta argentinana Yunck.
Cuscuta aristeguietae Yunck.
Cuscuta australis R. Br.: Parasitic Plant Connection
Cuscuta babylonica Aucher ex Choisy: Parasitic Plant Connection
Cuscuta balansae Boiss. & Reut. ex Yunck.: Parasitic Plant Connection
Cuscuta bifurcata Yunck.
Cuscuta bella Yunck.
Cuscuta blepharolepis Welw. ex Hiern.
Cuscuta boldinghii Urb.: Botanypictures.com
Cuscuta boliviana Yunck.
Cuscuta bonafortunae Costea & I. Garcia: Phytoimages
Cuscuta brachycalyx (Yunck.) Yunck.: CalPhotos
Cuscuta bracteata Yunck.
Cuscuta brevistyla Braun
Cuscuta chapalana Yunck.: Phytoimages
Cuscuta californica Hook. & Arn.: CalPhotos
Cuscuta campestris Yunck.: Parasitic Plant Connection; Plantarium; Phytoimages; CalPhotos; Schede di Botanica
Cuscuta capitata Roxb.
Cuscuta carnosa Costea & Stefanovic
Cuscuta cassytoides Nees ex Engelm.
Cuscuta castroviejoi M.A. Garcia
Cuscuta cephalanthi Engelm.: Parasitic Plant Connection; IPM images
Cuscuta chapalana Yunck.: Phytoimages
Cuscuta chilensis Ker Gawl.: Phytoimages; Parasitic Plant Connection; ChileFlora
Cuscuta chinensis Lam.: Flora of China; Botany Photo of the Day, UBC
Cuscuta choisiana Yunck.
Cuscuta cockerellii Yunck.
Cuscuta compacta Juss.: Parasitic Plant Connection
Cuscuta corniculata Engelm.
Cuscuta coryli Engelm. PBASE (J. McNeal)
Cuscuta corymbosa Ruiz & Pavon.: Phytoimages
Cuscuta costaricensis Yunck.; Phytoimages
Cuscuta cotijana Costea & I. Garcia; Phytoimages
Cuscuta cozumeliensis Yunck.
Cuscuta cristata Engelm.
Cuscuta cucullata Yunck.
Cuscuta cuspidata Engelm.: Parasitic Plant Connection
Cuscuta decipiens Yunck.
Cuscuta deltoidea Yunck.
Cuscuta dentatasquamata Yunck.
Cuscuta denticulata Engelm.: CalPhotos
Cuscuta desmouliniana Yunck. Phytoimages
Cuscuta draconella Costea & Stefanovic
Cuscuta epilinum Weihe: Parasitic Plant Connection; Schede di Botanica
Cuscuta epithymum (L.) L.: Parasitic Plant Connection; Schede di Botanica
Cuscuta erosa Yunck.: Phytoimages
Cuscuta europaea L.: Parasitic Plant Connection; PBASE; Plantarium; Schede di Botanica
Cuscuta exaltata Engelm.: Parasitic Plant Connection; PBASE (J. McNeal)
Cuscuta floribunda Kunth
Cuscuta flossdorfii Hicken
Cuscuta foetida Kunth: Flickr (Nancy.Rolando)
Cuscuta friesii Yunck.
Cuscuta gerrardii Baker
Cuscuta gigantea Griff.
Cuscuta glabrior (Engelm.) Yunck.: TAMU herbarium; Flickr (S. Hill)
Cuscuta globiflora Engelm.
Cuscuta globosa Ridley
Cuscuta globulosa Benth.
Cuscuta glomerata Choisy: Parasitic Plant Connection; PBASE (J. McNeal); Flickr (various authors); Richard Lutz – Iowa Plants;
Cuscuta goyaziana Yunck.
Cuscuta gracillima Engelm.: Phytoimages
Cuscuta grandiflora Kunth: Phytoimages; Parasitic Plant Connection; FossilFlowers.org ; WLU (photos by Jim Farfán: photo 1; photo 2; photo 3)
Cuscuta gronovii Willd. ex Schult.: Phytoimages; Parasitic Plant Connection
Cuscuta gymnocarpa Engelm.
Cuscuta harperi Small: PBASE: photo 1 and 2 (Joel McNeal); Flickr (Melody McClure)
Cuscuta haughtii Yunck.
Cuscuta haussknechtii Yunck.
Cuscuta hitchcockii Yunck.
Cuscuta howelliana Rubtzoff: Calphotos
Cuscuta hyalina Roth
Cuscuta incurvata Progel
Cuscuta indecora Choisy: Phytoimages; Parasitic Plant Connection; Arizona Wild Flowers; SEINet
Cuscuta insquamata Yunck.
Cuscuta jalapensis Schltdl. Picasa (Art Vogel); Phytoimages
Cuscuta japonica Choisy: Plantarium; Parasitic Plant Connection
Cuscuta jepsonii Yunck.
Cuscuta kilimanjari Oliv.
Cuscuta kurdica Engelm.
Cuscuta lacerata Yunck.
Cuscuta legitima Costea & Stefanovic: Phytoimages;
Cuscuta lehmanniana Bunge: Plantarium
Cuscuta leptantha Engelm.: CalPhotos
Cuscuta letourneuxii Trabut
Cuscuta liliputana Costea & Stefanovic
Cuscuta lindsayi Wiggins: Phytoimages
Cuscuta lucidacarpa Yunck.
Cuscuta lupuliformis Krock.: Parasitic Plant Connection; Plantarium; PBASE
Cuscuta macrocephala W. Schaffn. ex Yunck.
Cuscuta macvaughii Yunck.
Cuscuta membranacea Yunck.
Cuscuta mexicana Yunck.
Cuscuta micrantha Choisy
Cuscuta microstyla Engelm.: Phytoimages
Cuscuta mitriformis Engelm. FossilFlowers.org ; Picasa (Ron Parsons)
Cuscuta monogyna Vahl: Parasitic Plant Connection; Plantarium
Cuscuta natalensis Baker
Cuscuta nevadensis I. M. Johnst.
Cuscuta nitida E. Mey. ex Choisy
Cuscuta nivea M.A.Garcia: Parasitic Plant Connection
Cuscuta obtusata Trab.
Cuscuta obtusiflora Kunth: Phytoimages
Cuscuta occidentalis Millsp.: CalPhotos
Cuscuta odontolepis Engelm.;
Cuscuta odorata Ruiz & Pav.: Marjin van den Brink’s photos
Cuscuta orbiculata Yunck.
Cuscuta ortegana Yunck.: Phytoimages
Cuscuta pacifica Costea & M.A.R Wright: CalPhotos; Parasitic Plant Connection; Phytoimages
Cuscuta paitana Yunck.
Cuscuta palaestina Boiss.: Parasitic Plant Connection
Cuscuta palustris Yunck.
Cuscuta parodiniana Yunck.
Cuscuta partita Choisy
Cuscuta parviflora Engelm.
Cuscuta pauciflora Phil.: WLU: photos 1; photo 2; photo 3
Cuscuta pedicellata Ledeb.: Parasitic Plant Connection
Cuscuta pentagona Engelm.;
Cuscuta peruviana Yunck.
Cuscuta planiflora Ten.: FloradeCanarias.org; Plantarium
Cuscuta plattensis A Nelson
Cuscuta platyloba Progel
Cuscuta polyanthemos W. Schaffn. ex Yunck.
Cuscuta polygonorum Engelm.
Cuscuta potosina W. Schaffn. ex S. Watson
Cuscuta prismatica Pav. ex Choisy
Cuscuta pulchella Engelm.
Cuscuta punana Costea & Stefanovic
Cuscuta purpurata Phil.: Flickr (Jardin Botanico Nacional de Viña); Flickr: photo 1; photo 2 (Andrea Ugarte); WLU; Phytoimages;
Cuscuta purpusii Yunck.
Cuscuta pusilla Phil. ex Yunck.
Cuscuta racemosa Mart.: FloraSBS
Cuscuta rausii M.A. Garcia: Parasitic Plant Connection
Cuscuta reflexa Roxb.: Parasitic Plant Connection; Calphotos; Convolvulaceae unlimited; Flickr (T. Rodd)
Cuscuta rojasii Hunziker
Cuscuta rostrata Shuttlew. ex Engelm. & A. Gray: Parasitic Plant Connection; PBASE (J. McNeal)
Cuscuta rotundiflora Hunziker
Cuscuta rubella Yunck.
Cuscuta rugosiceps Yunck.
Cuscuta runyonii Yunck.: wildflower.org
Cuscuta salina Engelm.: CalPhotos
Cuscuta sandwichiana Choisy: Parasitic Plant Connection; Flickr (J. Nielsen); Morphbank;
Cuscuta schlechteri Yunck.
Cuscuta serrata Yunck. Mauricio Mercadante’s Flora do Cerrado (Flickr)
Cuscuta squamata Engelm.: Parasitic Plant Connection
Cuscuta sidarum Liemb.
Cuscuta somaliensis Yunck.: Parasitic Plant Connection
Cuscuta sphaerogyna Engelm.
Cuscuta stenolepis Engelm.
Cuscuta stenoloba Bornmuller & Scwarz
Cuscuta strobilacea Liebm. Phytoimages
Cuscuta stuckertii Yunck.
Cuscuta subinclusa Durand & Hilgard: CalPhotos
Cuscuta suaveolens Ser.
Cuscuta suksdorfii Yunck.: CalPhotos
Cuscuta tasmanica Engelm.: Parasitic Plant Connection; Flickr (davidtng); Flickr (Nuytsia@Tas)
Cuscuta tatei Yunck.
Cuscuta timorensis Decaisne
Cuscuta tinctoria Mart. ex Engelm.: Phytoimages
Cuscuta tinei Insenga
Cuscuta trichostyla Engelm.
Cuscuta triumvirati